go.net/ipv4: skip ancillary data socket option tests on non-supported kernels

It seems that old darwin kernels don't handle IP_RECVIF, IP_RECVDSTADDR correctly.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/158030043

ipv4/multicast_test.go

@@ -62,7 +62,10 @@ func TestPacketConnReadWriteMulticastUDP(t *testing.T) {
 	cf := ipv4.FlagTTL | ipv4.FlagDst | ipv4.FlagInterface
 
 	for i, toggle := range []bool{true, false, true} {
-		if err := p.SetControlMessage(cf, toggle); err != nil && !protocolNotSupported(err) {
+		if err := p.SetControlMessage(cf, toggle); err != nil {
+			if protocolNotSupported(err) {
+				t.Skipf("not supported on %q", runtime.GOOS)
+			}
 			t.Fatalf("ipv4.PacketConn.SetControlMessage failed: %v", err)
 		}
 		if err := p.SetDeadline(time.Now().Add(200 * time.Millisecond)); err != nil {
@@ -135,7 +138,10 @@ func TestPacketConnReadWriteMulticastICMP(t *testing.T) {
 		if err != nil {
 			t.Fatalf("icmp.Message.Marshal failed: %v", err)
 		}
-		if err := p.SetControlMessage(cf, toggle); err != nil && !protocolNotSupported(err) {
+		if err := p.SetControlMessage(cf, toggle); err != nil {
+			if protocolNotSupported(err) {
+				t.Skipf("not supported on %q", runtime.GOOS)
+			}
 			t.Fatalf("ipv4.PacketConn.SetControlMessage failed: %v", err)
 		}
 		if err := p.SetDeadline(time.Now().Add(200 * time.Millisecond)); err != nil {
@@ -228,7 +234,10 @@ func TestRawConnReadWriteMulticastICMP(t *testing.T) {
 			Protocol: 1,
 			Dst:      dst.IP,
 		}
-		if err := r.SetControlMessage(cf, toggle); err != nil && !protocolNotSupported(err) {
+		if err := r.SetControlMessage(cf, toggle); err != nil {
+			if protocolNotSupported(err) {
+				t.Skipf("not supported on %q", runtime.GOOS)
+			}
 			t.Fatalf("ipv4.RawConn.SetControlMessage failed: %v", err)
 		}
 		if err := r.SetDeadline(time.Now().Add(200 * time.Millisecond)); err != nil {

ipv4/unicast_test.go

@@ -113,7 +113,10 @@ func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
 	cf := ipv4.FlagTTL | ipv4.FlagDst | ipv4.FlagInterface
 
 	for i, toggle := range []bool{true, false, true} {
-		if err := p.SetControlMessage(cf, toggle); err != nil && !protocolNotSupported(err) {
+		if err := p.SetControlMessage(cf, toggle); err != nil {
+			if protocolNotSupported(err) {
+				t.Skipf("not supported on %q", runtime.GOOS)
+			}
 			t.Fatalf("ipv4.PacketConn.SetControlMessage failed: %v", err)
 		}
 		p.SetTTL(i + 1)
@@ -173,7 +176,10 @@ func TestPacketConnReadWriteUnicastICMP(t *testing.T) {
 		if err != nil {
 			t.Fatalf("icmp.Message.Marshal failed: %v", err)
 		}
-		if err := p.SetControlMessage(cf, toggle); err != nil && !protocolNotSupported(err) {
+		if err := p.SetControlMessage(cf, toggle); err != nil {
+			if protocolNotSupported(err) {
+				t.Skipf("not supported on %q", runtime.GOOS)
+			}
 			t.Fatalf("ipv4.PacketConn.SetControlMessage failed: %v", err)
 		}
 		p.SetTTL(i + 1)
@@ -257,7 +263,10 @@ func TestRawConnReadWriteUnicastICMP(t *testing.T) {
 			Protocol: 1,
 			Dst:      dst.IP,
 		}
-		if err := r.SetControlMessage(cf, toggle); err != nil && !protocolNotSupported(err) {
+		if err := r.SetControlMessage(cf, toggle); err != nil {
+			if protocolNotSupported(err) {
+				t.Skipf("not supported on %q", runtime.GOOS)
+			}
 			t.Fatalf("ipv4.RawConn.SetControlMessage failed: %v", err)
 		}
 		if err := r.SetWriteDeadline(time.Now().Add(100 * time.Millisecond)); err != nil {