OpenRC uses mount -a -O [no]_netdev to specify when to mount network/non-network file systems on Linux. Busybox's internal mount command should probably support this option. This would also make the mount command more compatible with util-linux's mount command. Thanks, William
It seems busybox-1.21.0 mount has -O (capital O) option support. I can do mount -a -O no_netdev and and mount -a -O _netdev with mount honoring _netdev in fstab. And looking at the source code, version 1.20.2 seems to be able too.
I am closing this based on the previous comment.