dial w sockopt

func CustomDial(network, addr string) (net.Conn, error) {
	if network != "tcp" {
		fmt.Println("network is ", network)
		panic("CustomDial can work only with tcp")
	}
	sd, err := syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, 0)
	if err != nil {
		return nil, fmt.Errorf("cant create socket: %#v\n", err)
	}
	/* window clamp */
	err = syscall.SetsockoptInt(sd, syscall.IPPROTO_TCP,
		TCP_WINDOW_CLAMP, BUFF_4K)
	if err != nil {
		return nil, fmt.Errorf("cant set window clamp: %#v\n", err)
	}

	/* rcv buff */
	err = syscall.SetsockoptInt(sd, syscall.SOL_SOCKET,
		syscall.SO_RCVBUF, BUFF_8K)
	if err != nil {
		return nil, fmt.Errorf("cant set rcvbuff: %#v\n", err)
	}

	/* mss */
	err = syscall.SetsockoptInt(sd, syscall.IPPROTO_TCP,
		syscall.TCP_MAXSEG, 1450)
	if err != nil {
		return nil, fmt.Errorf("cant set mss: %#v\n", err)
	}

	addrFields := strings.Split(addr, ":")
	if len(addrFields) != 2 {
		return nil, fmt.Errorf("addr doesnt contain port field")
	}
	port, err := strconv.Atoi(addrFields[1])
	if err != nil {
		return nil, fmt.Errorf("cant convert port to int: %#v\n", err)
	}
	ipaddr, err := net.ResolveIPAddr("ip", addrFields[0])
	if err != nil {
		return nil, fmt.Errorf("cant resolve ip addr: %#v\n", err)
	}
	if len(ipaddr.IP) == V4_ADDR_LEN {
		var ipv4addr [V4_ADDR_LEN]byte
		for cntr := 0; cntr < V4_ADDR_LEN; cntr++ {
			ipv4addr[cntr] = ipaddr.IP[cntr]
		}
		sa := syscall.SockaddrInet4{
			Addr: ipv4addr,
			Port: port,
		}
		err := syscall.Connect(sd, &sa)
		if err != nil {
			return nil, fmt.Errorf("cant connect to remote addr: %#v\n", err)
		}
	} else if len(ipaddr.IP) == V6_ADDR_LEN {
		var ipv6addr [V6_ADDR_LEN]byte
		for cntr := 0; cntr < V6_ADDR_LEN; cntr++ {
			ipv6addr[cntr] = ipaddr.IP[cntr]
		}
		sa := syscall.SockaddrInet6{
			Addr: ipv6addr,
			Port: port,
		}
		err := syscall.Connect(sd, &sa)
		if err != nil {
			return nil, fmt.Errorf("cant connect to remote addr: %#v\n", err)
		}
	}
	f := os.NewFile(uintptr(sd), "")
	c, err := net.FileConn(f)
	f.Close()
	return c, err
}