network: Fix network layout selection

Previously the bridged layout could be set in the NIC details dialog,
but it couldn't be switched back to the direct (bridgeless) mode.
Now the bridged mode can be turned on and off as expected.

Change-Id: Ib70c81ca70abeb84393e2a88b2287b8e208d2104
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=981097
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>