Fix for bug 902175
Fix for bug 902175

We can't use merge if we're removing a field from the port object so use add
instead.  Also, pass the session to port_get so that we don't run into the
"this port is already bound to session x" error.

Change-Id: I54a8484c8f6429ad18fb0c5e088720d21fc16299

gkotton/vmware-nsx,gkotton/vmware-nsx