webadmin: Update Tx/Rx in Host Interfaces subtab

Was formerly disabled due to exceptions being thrown; at the moment
the values seem to be updated well and without causing any trouble.

Change-Id: I68e37c6c37480eca3512c84b06690a18aabea2eb
Bug-Url: https://bugzilla.redhat.com/746458
Signed-off-by: Lior Vernia <lvernia@redhat.com>