Floating IP agent gateway ports are created for each external network
for each node where DVR L3 agent is running and where there is some FIP
from the ext_net.
But even, if L3 agent is removed (e.g. when scaling down the cluster),
such floating IP gateway port is never removed so it consumes IP address
from the external network.
With this patch when the DVR L3 agent is deleted, all such fip gateway
ports owned by that agent will be deleted.
When new L3 agent is created (registered in the DB), Neutron will check
if there are any floating IPs on that host and will recreate such FIP
gateway ports for it.
Closes-Bug: #1891360
Change-Id: If6ef990baf039c556d7420962ac4c54608711f06
(cherry picked from commit 8cc7c0cf7a)
4bdfc71145