net: enable IPv6 tests on Windows

Also removes redundant tests that run Go 1.0 non-IPv6 support
Windows code on IPv6 enabled Windows kernels.

R=alex.brainman, golang-dev, bradfitz, dave
CC=golang-dev
https://golang.org/cl/7812052

src/pkg/net/multicast_test.go

@@ -93,7 +93,7 @@ var ipv6MulticastListenerTests = []struct {
 // port.
 func TestIPv6MulticastListener(t *testing.T) {
 	switch runtime.GOOS {
-	case "plan9", "solaris", "windows":
+	case "plan9", "solaris":
 		t.Skipf("skipping test on %q", runtime.GOOS)
 	}
 	if !supportsIPv6 {

src/pkg/net/unicast_posix_test.go

@@ -45,7 +45,7 @@ var listenerTests = []struct {
 // same port.
 func TestTCPListener(t *testing.T) {
 	switch runtime.GOOS {
-	case "plan9", "windows":
+	case "plan9":
 		t.Skipf("skipping test on %q", runtime.GOOS)
 	}
 
@@ -68,66 +68,9 @@ func TestTCPListener(t *testing.T) {
 // listener with same address family, same listening address and
 // same port.
 func TestUDPListener(t *testing.T) {
-	switch runtime.GOOS {
-	case "plan9", "windows":
-		t.Skipf("skipping test on %q", runtime.GOOS)
-	}
-
-	toudpnet := func(net string) string {
-		switch net {
-		case "tcp":
-			return "udp"
-		case "tcp4":
-			return "udp4"
-		case "tcp6":
-			return "udp6"
-		}
-		return "<nil>"
-	}
-
-	for _, tt := range listenerTests {
-		if tt.wildcard && (testing.Short() || !*testExternal) {
-			continue
-		}
-		if tt.ipv6 && !supportsIPv6 {
-			continue
-		}
-		tt.net = toudpnet(tt.net)
-		l1, port := usableListenPacketPort(t, tt.net, tt.laddr)
-		checkFirstListener(t, tt.net, tt.laddr+":"+port, l1)
-		l2, err := ListenPacket(tt.net, tt.laddr+":"+port)
-		checkSecondListener(t, tt.net, tt.laddr+":"+port, err, l2)
-		l1.Close()
-	}
-}
-
-func TestSimpleTCPListener(t *testing.T) {
-	switch runtime.GOOS {
-	case "plan9":
-		t.Skipf("skipping test on %q", runtime.GOOS)
-		return
-	}
-
-	for _, tt := range listenerTests {
-		if tt.wildcard && (testing.Short() || !*testExternal) {
-			continue
-		}
-		if tt.ipv6 {
-			continue
-		}
-		l1, port := usableListenPort(t, tt.net, tt.laddr)
-		checkFirstListener(t, tt.net, tt.laddr+":"+port, l1)
-		l2, err := Listen(tt.net, tt.laddr+":"+port)
-		checkSecondListener(t, tt.net, tt.laddr+":"+port, err, l2)
-		l1.Close()
-	}
-}
-
-func TestSimpleUDPListener(t *testing.T) {
 	switch runtime.GOOS {
 	case "plan9":
 		t.Skipf("skipping test on %q", runtime.GOOS)
-		return
 	}
 
 	toudpnet := func(net string) string {
@@ -146,7 +89,7 @@ func TestSimpleUDPListener(t *testing.T) {
 		if tt.wildcard && (testing.Short() || !*testExternal) {
 			continue
 		}
-		if tt.ipv6 {
+		if tt.ipv6 && !supportsIPv6 {
 			continue
 		}
 		tt.net = toudpnet(tt.net)
@@ -231,7 +174,7 @@ func TestDualStackTCPListener(t *testing.T) {
 		t.Skipf("skipping test on %q", runtime.GOOS)
 	}
 	if !supportsIPv6 {
-		return
+		t.Skip("ipv6 is not supported")
 	}
 
 	for _, tt := range dualStackListenerTests {
@@ -263,7 +206,7 @@ func TestDualStackUDPListener(t *testing.T) {
 		t.Skipf("skipping test on %q", runtime.GOOS)
 	}
 	if !supportsIPv6 {
-		return
+		t.Skip("ipv6 is not supported")
 	}
 
 	toudpnet := func(net string) string {