fff-network: Commit only network

Since we change only the network part of uci, we only need to
commit this part and not the whole config five times.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>
- Rebased
Signed-off-by: Tim Niemeyer <tim@tn-x.org>