Update the ports list.

def update(self):
        """Update the ports list."""
        if self.input_method == 'local':
            # Only refresh:
            # * if there is not other scanning thread
            # * every refresh seconds (define in the configuration file)
            if self._thread is None:
                thread_is_running = False
            else:
                thread_is_running = self._thread.isAlive()
            if self.timer_ports.finished() and not thread_is_running:
                # Run ports scanner
                self._thread = ThreadScanner(self.stats)
                self._thread.start()
                # Restart timer
                if len(self.stats) > 0:
                    self.timer_ports = Timer(self.stats[0]['refresh'])
                else:
                    self.timer_ports = Timer(0)
        else:
            # Not available in SNMP mode
            pass

        return self.stats