code: def flow_removed_handler(self, evt):
          
          msg = evt.msg
          datapath = msg.datapath
          ofproto = datapath.ofproto
          dpid = datapath.id
          match = msg.match
          if ofproto.OFP_VERSION == ofproto_v1_0.OFP_VERSION:
              port = match.in_port
              dl_type = match.dl_type
          else:
              port = match['in_port']
              dl_type = match['eth_type']
          if ether.ETH_TYPE_SLOW != dl_type:
              return
          self.logger.info(
              "SW=%s PORT=%d LACP exchange timeout has occurred.",
              dpid_to_str(dpid), port)
          self._set_slave_enabled(dpid, port, False)
          self._set_slave_timeout(dpid, port, 0)
          self.send_event_to_observers(
              EventSlaveStateChanged(datapath, port, False))
docs: FlowRemoved event handler. when the removed flow entry was
          for LACP, set the status of the slave i/f to disabled, and
          send a event.