Golang で net/http クライアントに IPv4/IPv6 を使用させるにはどうすればよいですか?

<code class="go">import (
    "errors"
    "fmt"
    "net"
    "net/http"
    "syscall"
    "time"
)

func modifiedTransport() {
    var myTransport = &http.Transport{
        DialContext: (&net.Dialer{
            Timeout:   30 * time.Second,
            KeepAlive: 30 * time.Second,
            DualStack: false,
            Control: func(network, address string, c syscall.RawConn) error {
                if network == "ipv4" {
                    // Here you can return an error to prevent connection establishment over IPv4.
                    return errors.New("ipv4 connections are not allowed")
                }
                return nil
            },
        }).DialContext,
        MaxIdleConns:          100,
        IdleConnTimeout:       90 * time.Second,
        TLSHandshakeTimeout:   10 * time.Second,
        ExpectContinueTimeout: 1 * time.Second,
    }

    var myClient = http.Client{Transport: myTransport}
    resp, err := myClient.Get("http://www.github.com")
    if err != nil {
        fmt.Println("Request error:", err)
        return
    }

    var buffer = make([]byte, 1000)
    resp.Body.Read(buffer)
    fmt.Println(string(buffer))
}</code>