[99s-extend] Stop ranch listeners without dropping connections

[Roger Lipscombe]

Using ranch, is there any way to stop the listener (and acceptors)
without dropping the existing connections?

I ask because I'd like to start another instance of my server on the
same box and have the old instance continue to handle its existing
connections for a while.

It looks to me that if I call ranch:stop_listener, it'll kill the
ranch_listener_sup, which will also kill the ranch_conns_sup (and the
existing connections).

If I manually do a supervisor:terminate_child(ListenerPid,
ranch_acceptors_sup), the acceptors go away, but the socket is still
open, which means that I can't start another instance of my server.

Thoughts?