There's a pool of tcp sockets for communicating with clients.  We limit the
number to (serv->sv_nrthreads+3)*20; so a server with 8 threads, for example,
will be limited to 220 active tcp connections; more and we start just closing
old sockets.

Note that the SVC_SOCK_TEMPORARY flag is set on sockets purely to keep track of
this number; we decrement sv_tmpcnt on close iff this flag is set.