connect: implement TCP Fast Open for OS X

  /* Connect TCP sockets, bind UDP */

  if(!isconnected && (conn->socktype == SOCK_STREAM)) {

    if(conn->bits.tcp_fastopen) {

#if defined(CONNECT_DATA_IDEMPOTENT) /* OS X */

      sa_endpoints_t endpoints;

      endpoints.sae_srcif = 0;

      endpoints.sae_srcaddr = NULL;

      endpoints.sae_srcaddrlen = 0;

      endpoints.sae_dstaddr = &addr.sa_addr;

      endpoints.sae_dstaddrlen = addr.addrlen;

      rc = connectx(sockfd, &endpoints, SAE_ASSOCID_ANY,

                    CONNECT_RESUME_ON_READ_WRITE | CONNECT_DATA_IDEMPOTENT,

                    NULL, 0, NULL, NULL);

#endif

    }

    else {

      rc = connect(sockfd, &addr.sa_addr, addr.addrlen);

    }

    if(-1 == rc)

      error = SOCKERRNO;

  }