[det]tcp_listen(+SocketId,
+BackLog)Tells, after tcp_bind/2, the
socket to listen for incoming requests for connections. Backlog
indicates how many pending connection requests are allowed. Pending
requests are requests that are not yet acknowledged using tcp_accept/3.
If the indicated number is exceeded, the requesting client will be
signalled that the service is currently not available. A commonly used
default value for Backlog is 5.