It is enough if one network interface is online, there is no need to wait for all of them.
Without this, when connecting with Wi-Fi and leaving Ethernet disconnected, the network-online.target will get unnecessarily delayed.
configs/releng/airootfs/etc/systemd/system/multi-user.target.wants/iwd.service:
Adding a symlink to /usr/lib/systemd/system/iwd.service to enable iwd in
airootfs (and thus on the image).
Closes#18