unix_listener
sock = unix_listener(fwd->listen_path, SSH_LISTEN_BACKLOG,
int unix_listener(const char *, int, int);
muxserver_sock = unix_listener(options.control_path, 64, 0);
sock = unix_listener(auth_sock_name, SSH_LISTEN_BACKLOG, 0);
sock = unix_listener(socket_name, SSH_LISTEN_BACKLOG, 0);