zebra: fix interface lookup for vrf configuration

zebra: fix interface lookup for vrf configuration

Ticket:CM-9073
Reviewed By: sharpd
Testing Done:Manual, see ticket

Changed logic when "interface swpxx <vrf foo>" entered so that:

1. it matches when the command is entered without a vrf but the interface already exists in a vrf.
2. If the command is entered with a vrf name that is different than is defined by the kernel, the command is rejected.
3. If the call is made from other than the vty session, believe the new information and update the vrf accordingly.