bug#53381: wireguard service can fail on boot by starting before DNS is ready

[Nathan Dehnel]

As shown here on boot:

[#] ip link add test type wireguard
[#] wg setconf test /dev/fd/63
Name or service not known: `<other server FQDN>:51820'
Configuration parsing error
[#] ip link delete dev test
failed to start service 'wireguard-test'

This can cause remote machines to become inaccessible.

Is there an equivalent of systemd-networkd-wait-online.service? Or
perhaps you would accept a patch to enable the "respawn?" service
method, so wireguard will eventually connect once DNS is ready?