code: def packet_in_handler(self, evt):
          
          req_pkt = packet.Packet(evt.msg.data)
          if slow.lacp in req_pkt:
              (req_lacp, ) = req_pkt.get_protocols(slow.lacp)
              (req_eth, ) = req_pkt.get_protocols(ethernet.ethernet)
              self._do_lacp(req_lacp, req_eth.src, evt.msg)
          else:
              self.send_event_to_observers(EventPacketIn(evt.msg))
docs: PacketIn event handler. when the received packet was LACP,
          proceed it. otherwise, send a event.