webadmin: When vnic's property become disabled again it should be reseted

Some vnic's properties update is blocked if the vm is up and the vnic is
plugged.
Opening the update vnic dialog and changing the vnic to unplugged,
unblocks these properties.
Changing the vnic back to plugged should revert the changes done on these
properties.

Change-Id: I39d70d8948f32e8e6f45f2d1eba5a3d26bb04975
Bug-Url: https://bugzilla.redhat.com/909852
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>