sock_connect_mptcp
fd = sock_connect_mptcp(cfg_host, cfg_port, cfg_sock_proto, &peer, fd_in, &winfo);
fd = sock_connect_mptcp("127.0.0.1", "15432", proto_tx);
fd = sock_connect_mptcp("::1", "15432", proto_tx);
fd = sock_connect_mptcp("127.0.0.1", "15432", IPPROTO_MPTCP);
fd = sock_connect_mptcp("::1", "15432", IPPROTO_MPTCP);