add a -tls flag to the example client and server

This will add the WIP TLS version as the preferred supported version. It
is intended for developing and testing of IETF QUIC.

example/client/main.go

@@ -7,12 +7,15 @@ import (
 	"net/http"
 	"sync"
 
+	quic "github.com/lucas-clemente/quic-go"
 	"github.com/lucas-clemente/quic-go/h2quic"
+	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/utils"
 )
 
 func main() {
 	verbose := flag.Bool("v", false, "verbose")
+	tls := flag.Bool("tls", false, "activate support for IETF QUIC (work in progress)")
 	flag.Parse()
 	urls := flag.Args()
 
@@ -23,8 +26,15 @@ func main() {
 	}
 	utils.SetLogTimeFormat("")
 
+	versions := protocol.SupportedVersions
+	if *tls {
+		versions = append([]protocol.VersionNumber{protocol.VersionTLS}, versions...)
+	}
+
 	hclient := &http.Client{
-		Transport: &h2quic.RoundTripper{},
+		Transport: &h2quic.RoundTripper{
+			QuicConfig: &quic.Config{Versions: versions},
+		},
 	}
 
 	var wg sync.WaitGroup