webadmin: Added check to prevent no-op case

Adding a NIC to the bond already containing it wasn't marked as a
no-op so it was displayed as a legitimate operation.

Change-Id: Iebff9f9e3b5cd9973cfbebe307ae75a2e5d96a67
Bug-Url: https://bugzilla.redhat.com/1045656
Bug-Url: https://bugzilla.redhat.com/1045658
Signed-off-by: Lior Vernia <lvernia@redhat.com>