Comment 4 for bug 1522980

Change https://review.openstack.org/#/c/255237/ sets up flood flows between slave agents and other agents.

But when l2 agent in slave node is restarted
1) existing flows in slave(created by change 255237) will be deleted.
2) then l2 agent calls update_device_up for router interface port
3) update_device_up won't call update_port_status as
   port_bound_to_host fails(port is bound to master host and not this slave host)
4) hence l2pop driver is not called for router interface port,
   so l2pop driver can't notify network ports to slave node.
5) Because of this, slave nodes can't have flood entries to other agents
If neutron server is down at this time and this slave becomes master
at the same time, this new master router can't communicate with
vms through the router interface port.