In the current case (only "direct" lobby backend, i.e. connect to a
server directly), lobby and game are always on the same server anyway..
It used to send the IP of the first network interface.. that kinda works
on Windows and FreeBSD in LANs (i.e. not over the internet or even
behind a NAT), but not at all on Linux, because the first device seems
to be the loopback device there (at least on my machine)..
Now it sends net_ip (so it should even work behind NAT) or, if net_ip is
set to "localhost" (the default), 0.0.0.0 is sent, which the client
interprets as "just use the IP of the lobby you're already connected to"
And suddenly hosting a server on linux works at least locally
(with client and server on the same machine).
Even though there are still strange bugs (massive lags in one
direction, doesn't work in LAN), at least it works at all now.
