Fix for OPENSTACK-1244
Fix for OPENSTACK-1244

Trying to update a port's fixed_ip property to a different value than the
current will result in a bad request.

Change-Id: I1597b2ca8cd7733f83db9aa4d9151ed93099990e
Closes-Bug: OPENSTACK-1244

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