After 85843da (container: Make "waydroid-net.sh start" failure fatal)
this could result always failing to start unless you ran
"waydroid-net.sh stop" manually first; perhaps this should always be
stopped upon encountering errors?
The "default to waydroid0" was broken as awk never returned a non-zero
exit code if the file exists but no match was found. Also account for
the key being named lxc.network.link on older LXC versions so one still
has the ability to have a flexible Waydroid network configuration.
