Make strict check on gateway-ip for VSD-managed subnets
Make strict check on gateway-ip for VSD-managed subnets

Change-Id: I56ad66d4df8f278e4030f56656ea5f26b0817738
Depends-On: I1b75b67ea4a5a1682143ea5f10899a5008af1cdc
Closes-Bug: PROD-9860

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