webadmin: If the vnic is unplugged, all its fields should be enabled

If the vnic is unplugged, all its properties can be updated.
The bug was that if while editing the vnic it was changed to unplugged,
the editing of some properties was blocked.

Change-Id: I7f652e88df37ffb48500a9e86c361d3f8964afe1
Bug-Url: https://bugzilla.redhat.com/906434
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>