Move UNIX services from net_server to launch_daemon

[X512]

This is hrev53917.

UNIX services like sshd are currently managed by net_server, but it should be managed by launch_roster. launch_roster seems already have some UNIX services support like sending SIGINT signal on stop.

[pulkomandy]

I think the original idea of having them in net_server was to do something a bit like inetd: the net_server would watch for incoming tcp/udp connections and start the services on-demand. But I think net_server currently doesn't implement this, and launch_daemon does something somewhat similar for Be ports, I see no reason it couldn't do it for sockets as well?

[waddlesplash]

Launch daemon already has a "network up" trigger, so, yes, that sounds fine.