Set WoL when there's no IP

[alkisg]

When a standalone (non-LTSP) client boots, it's possible that epoptes-client will be started before networking.
And if SERVER=some-ip or some entry from /etc/hosts, then the epoptes-client.wait_for_dns function won't wait until DNS is up.
In that case, the current epoptes-client.apply_wol function can't detect the interface that will be used to contact the epoptes server, so it doesn't enable WoL for any interface.

One solution could be to transform wait_for_dns into wait_for_server_ip_reachable (using ip r get ...).
Another solution could be to enable WoL in all interfaces anyway; I can't think of any reason we'd prefer to enable WoL only in a specific interface.

[alkisg]

Closed by GSoC 2023 Epoptes improvements #204.
Please test if the proposed PPA build resolves this issue.