unix: fix EMFILE busy loop
unix: fix EMFILE busy loop

Don't spin in epoll_wait() / kevent() / port_getn() / etc. when we can't
accept() a new connection due to having reached the file descriptor limit.
Pass the error to the connection_cb and let the libuv user deal with it.

urbit/archaeology2,unknownbrackets/maxcso,urbit/archaeology2,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2