webadmin: Fix exception related to display network warning

ClassCastException, probably due to misunderstanding of the network
operations.

Change-Id: Iac63576d8e15bdae47ec0e08ae2b64395adc4765
Bug-Url: https://bugzilla.redhat.com/1078836
Signed-off-by: Lior Vernia <lvernia@redhat.com>