Close idle rpc/tcp sockets

We split the list of sv_allsocks into two, one
of permanent sockets (udp, tcp listener) and one
of temporary sockets (tcp data).

Whenever we complete a successful receive on a temp socket,
it gets pushed to the end of the list.

Whenever a thread wants to do something, it first checks if
the oldest temp socket has not has a receive for 6 mintutes
(should possibly be configurable).  It so, we simulate
a close.

Finally we make sure that threads wake up every few minutes
so that if the server is completely idle, all temp
sockets will get closed.