webadmin: Fixed MTU/VLAN in Networks/General subtab

Commas no longer appear as separators in large numbers.

Change-Id: Ia267b9b4dabde560fc24ef4334df0868f1a2a13c
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=891902
Signed-off-by: Lior Vernia <lvernia@redhat.com>