add ipv6 to xnet.StackAsync (#107)

* add ipv6 to xnet.StackAsync

* dns improvements

* improve DNS workings of StackAsync

* add tentative ICMPv6

* work on prefixes and fix some small bugs, plan UDP/TCP6

* fix bugs in StackAsync and ipv4.Prefix.Contains

* update arpsubtable

* completely remove legacy internet.StackIP for StackIPv4/v6

* ipv4/ipv6 tcp/udp

* add TCP6/UDP6 dialing APIs

* add xnet.Stack6 interface

* more ipv6 integration into StackAsync; various tweaks to lneto and documentation+TODOs

* add stack6 tests

* replace netip.Prefix with ipv4.Prefix where it makes sense

x/xnet/xnet_bench_test.go

@@ -35,8 +35,8 @@ func BenchmarkARPExchange(b *testing.B) {
 		b.Fatal(err)
 	}
 	// Set gateways so ethernet frames are properly addressed.
-	c1.SetGateway6(c2.HardwareAddress())
-	c2.SetGateway6(c1.HardwareAddress())
+	c1.SetGatewayHardwareAddr(c2.HardwareAddr())
+	c2.SetGatewayHardwareAddr(c1.HardwareAddr())
 
 	var buf [frameSize]byte
 
@@ -104,8 +104,8 @@ func BenchmarkTCPHandshake(b *testing.B) {
 	if err != nil {
 		b.Fatal(err)
 	}
-	sv.SetGateway6(client.HardwareAddress())
-	client.SetGateway6(sv.HardwareAddress())
+	sv.SetGatewayHardwareAddr(client.HardwareAddr())
+	client.SetGatewayHardwareAddr(sv.HardwareAddr())
 
 	buf := make([]byte, MTU*4)
 	err = clconn.Configure(tcp.ConnConfig{
@@ -130,7 +130,7 @@ func BenchmarkTCPHandshake(b *testing.B) {
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		// Setup connections.
-		err = sv.ListenTCP(svconn, svPort)
+		err = sv.ListenTCP4(svconn, svPort)
 		if err != nil {
 			b.Fatal(err)
 		}