ipv6: don't fail test on IPv6 disabled kernel

Change-Id: Ib667928f91808640021ea9d61bc5477824729655
Reviewed-on: https://go-review.googlesource.com/33253
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

ipv6/bpf_test.go

@@ -18,6 +18,9 @@ func TestBPF(t *testing.T) {
 	if runtime.GOOS != "linux" {
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
+	if !supportsIPv6 {
+		t.Skip("ipv6 is not supported")
+	}
 
 	l, err := net.ListenPacket("udp6", "[::1]:0")
 	if err != nil {