mwan3: update network.sh from upstream
Trying to run mwan3 2.7.6-1 on Turris 3.11.1 makes an error on service start.
network_get_metric does not exist
This function was added on 24.8.2018 in the upstream OpenWRT repo (in
Please update the base files, or at least
network.sh which wasn't updated for a long time.