Update network stats using the input method.

        Stats is a list of dict (one dict per interface)

def update(self):
        """Update network stats using the input method.

        Stats is a list of dict (one dict per interface)
        """
        # Init new stats
        stats = self.get_init_value()

        if self.input_method == 'local':
            # Update stats using the standard system lib

            # Grab network interface stat using the psutil net_io_counter method
            try:
                netiocounters = psutil.net_io_counters(pernic=True)
            except UnicodeDecodeError as e:
                logger.debug('Can not get network interface counters ({})'.format(e))
                return self.stats

            # Grab interface's status (issue #765)
            # Grab interface's speed (issue #718)
            netstatus = {}
            try:
                netstatus = psutil.net_if_stats()
            except OSError as e:
                # see psutil #797/glances #1106
                logger.debug('Can not get network interface status ({})'.format(e))

            # Previous network interface stats are stored in the network_old variable
            if not hasattr(self, 'network_old'):
                # First call, we init the network_old var
                try:
                    self.network_old = netiocounters
                except (IOError, UnboundLocalError):
                    pass
                return self.stats

            # By storing time data we enable Rx/s and Tx/s calculations in the
            # XML/RPC API, which would otherwise be overly difficult work
            # for users of the API
            time_since_update = getTimeSinceLastUpdate('net')

            # Loop over interfaces
            network_new = netiocounters
            for net in network_new:
                # Do not take hidden interface into account
                # or KeyError: 'eth0' when interface is not connected #1348
                if self.is_hide(net) or net not in netstatus:
                    continue
                try:
                    cumulative_rx = network_new[net].bytes_recv
                    cumulative_tx = network_new[net].bytes_sent
                    cumulative_cx = cumulative_rx + cumulative_tx
                    rx = cumulative_rx - self.network_old[net].bytes_recv
                    tx = cumulative_tx - self.network_old[net].bytes_sent
                    cx = rx + tx
                    netstat = {'interface_name': n(net),
                               'time_since_update': time_since_update,
                               'cumulative_rx': cumulative_rx,
                               'rx': rx,
                               'cumulative_tx': cumulative_tx,
                               'tx': tx,
                               'cumulative_cx': cumulative_cx,
                               'cx': cx,
                               # Interface status
                               'is_up': netstatus[net].isup,
                               # Interface speed in Mbps, convert it to bps
                               # Can be always 0 on some OSes
                               'speed': netstatus[net].speed * 1048576,
                               # Set the key for the dict
                               'key': self.get_key()
                               }
                except KeyError:
                    continue
                else:
                    # Append the interface stats to the list
                    stats.append(netstat)

            # Save stats to compute next bitrate
            self.network_old = network_new

        elif self.input_method == 'snmp':
            # Update stats using SNMP

            # SNMP bulk command to get all network interface in one shot
            try:
                netiocounters = self.get_stats_snmp(snmp_oid=snmp_oid[self.short_system_name],
                                                    bulk=True)
            except KeyError:
                netiocounters = self.get_stats_snmp(snmp_oid=snmp_oid['default'],
                                                    bulk=True)

            # Previous network interface stats are stored in the network_old variable
            if not hasattr(self, 'network_old'):
                # First call, we init the network_old var
                try:
                    self.network_old = netiocounters
                except (IOError, UnboundLocalError):
                    pass
            else:
                # See description in the 'local' block
                time_since_update = getTimeSinceLastUpdate('net')

                # Loop over interfaces
                network_new = netiocounters

                for net in network_new:
                    # Do not take hidden interface into account
                    if self.is_hide(net):
                        continue

                    try:
                        # Windows: a tips is needed to convert HEX to TXT
                        # http://blogs.technet.com/b/networking/archive/2009/12/18/how-to-query-the-list-of-network-interfaces-using-snmp-via-the-ifdescr-counter.aspx
                        if self.short_system_name == 'windows':
                            try:
                                interface_name = str(base64.b16decode(net[2:-2].upper()))
                            except TypeError:
                                interface_name = net
                        else:
                            interface_name = net

                        cumulative_rx = float(network_new[net]['cumulative_rx'])
                        cumulative_tx = float(network_new[net]['cumulative_tx'])
                        cumulative_cx = cumulative_rx + cumulative_tx
                        rx = cumulative_rx - float(self.network_old[net]['cumulative_rx'])
                        tx = cumulative_tx - float(self.network_old[net]['cumulative_tx'])
                        cx = rx + tx
                        netstat = {
                            'interface_name': interface_name,
                            'time_since_update': time_since_update,
                            'cumulative_rx': cumulative_rx,
                            'rx': rx,
                            'cumulative_tx': cumulative_tx,
                            'tx': tx,
                            'cumulative_cx': cumulative_cx,
                            'cx': cx}
                    except KeyError:
                        continue
                    else:
                        netstat['key'] = self.get_key()
                        stats.append(netstat)

                # Save stats to compute next bitrate
                self.network_old = network_new

        # Update the stats
        self.stats = stats

        return self.stats