repeated listen() calls on same sockets

[FreakyPenguin]

Looks like nginx (and possibly other applications) call listen on a socket more than once. Not exactly sure why, or what the sockets spec says should happen, but clearly this works on Linux so we should see if we can also handle this reasonably too.

[FreakyPenguin]

https://stackoverflow.com/questions/43078649/listen-called-on-socket-more-than-once-expected-behavior suggests this is used to adjust backlog queue length. So we could just ignore repeated call with a warning for now?