Support listen() for tcp wrapper

[stevenengler]

The logic generally follows the logic from src/main/host/syscall/socket.c.

shadow/src/main/host/syscall/socket.c

Lines 1072 to 1115 in e0cf195

	SysCallReturn syscallhandler_listen(SysCallHandler* sys,
	const SysCallArgs* args) {
	int sockfd = args->args[0].as_i64;
	int backlog = args->args[1].as_i64;
	trace("trying to listen on socket %i", sockfd);
	/* Get and validate the TCP socket. */
	TCP* tcp_desc = NULL;
	int errcode =
	_syscallhandler_validateTCPSocketHelper(sys, sockfd, &tcp_desc);
	if (errcode < 0) {
	return syscallreturn_makeDoneErrno(-errcode);
	}
	utility_debugAssert(tcp_desc);
	/* only listen on the socket if it is not used for other functions */
	if (!tcp_isListeningAllowed(tcp_desc)) {
	debug("Cannot listen on previously used socket %i", sockfd);
	return syscallreturn_makeDoneErrno(EOPNOTSUPP);
	}
	/* if we are already listening, just update the backlog and return 0. */
	if (tcp_isValidListener(tcp_desc)) {
	trace("Socket %i already set up as a listener; updating backlog", sockfd);
	tcp_updateServerBacklog(tcp_desc, backlog);
	return syscallreturn_makeDoneU64(0);
	}
	/* We are allowed to listen but not already listening, start now. */
	if (!legacysocket_isBound((LegacySocket*)tcp_desc)) {
	/* Implicit bind: bind to all interfaces at an ephemeral port. */
	trace("Implicitly binding listener socket %i", sockfd);
	errcode =
	_syscallhandler_bindHelper(sys, (LegacySocket*)tcp_desc, htonl(INADDR_ANY), 0, 0, 0);
	if (errcode < 0) {
	return syscallreturn_makeDoneErrno(-errcode);
	}
	}
	tcp_enterServerMode(
	tcp_desc, _syscallhandler_getHost(sys), _syscallhandler_getProcess(sys), backlog);
	return syscallreturn_makeDoneU64(0);
	}