Internal method.  Create libpcap devices
        for every network interface we care about and
        set them in non-blocking mode.

def _make_pcaps(self):
        '''
        Internal method.  Create libpcap devices
        for every network interface we care about and
        set them in non-blocking mode.
        '''
        self._pcaps = {}
        for devname,intf in self._devinfo.items():
            if intf.iftype == InterfaceType.Loopback:
                senddev = _RawSocket(devname, protocol=IPProtocol.UDP)
                self._localsend[devname] = senddev
            pdev = PcapLiveDevice(devname) 
            self._pcaps[devname] = pdev