webadmin: Adjust network panel height to fit arrows

The network panels were a little short compared to the arrows in the
Setup Networks dialog, which caused them to go out of alignment (more
noticeable as more networks are attached to the same interface).

Change-Id: I55a74d41c71e7153169e077fb61813b916e5d7c6
Bug-Url: https://bugzilla.redhat.com/1120660
Signed-off-by: Lior Vernia <lvernia@redhat.com>