Cherry-pick from stable/liberty: Fix for OPENSTACK-1153 When a router interface is added/deleted, if the subnet is from a providernet, ignore the bridge vports in that subnet and do not block the router interface add or delete action
Cherry-pick from stable/liberty: Fix for OPENSTACK-1153
When a router interface is added/deleted, if the subnet is from a providernet,
ignore the bridge vports in that subnet and do not block the router interface
add or delete action

Change-Id: I2356907ebb22daa55e682565ebaeaeeb4c51fc1e
Closes-Bug: OPENSTACK-1153

naveensan1/nuage-openstack-neutron,nuagenetworks/nuage-openstack-neutron,naveensan1/nuage-openstack-neutron,nuagenetworks/nuage-openstack-neutron