Built-in ROTT server

[fragglet]

Rise of the Triad is notoriously finicky about high latency connections, eg.

dosbox-staging/dosbox-staging#947

One solution that's apparently been used is to run a dedicated server in a separate DOSbox instance. ROTT's client-server architecture is actually pretty unhelpful for latency since it means that all game data has to go across the Internet twice (once to the "server" client, and then back to other clients). One solution would be to implement a ROTT dedicated server inside ipxbox. This would remove the need for a dedicated DOSbox instance and should also ~halve latency. Since the ROTT dedicated server is just doing packet forwarding (no actual gameplay simulation) this shouldn't be too difficult to implement.