ipv6: skip tests on aix, fuchsia and hurd

Also marks test helper functions.

Change-Id: I1baf791b6d4199699db20834fa6e1a3bd0733cf0
Reviewed-on: https://go-review.googlesource.com/c/net/+/167340
Run-TryBot: Mikio Hara <mikioh.public.networking@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
diff --git a/ipv6/multicastsockopt_test.go b/ipv6/multicastsockopt_test.go
index 9906e87..2cb2da2 100644
--- a/ipv6/multicastsockopt_test.go
+++ b/ipv6/multicastsockopt_test.go
@@ -26,7 +26,7 @@
 
 func TestPacketConnMulticastSocketOptions(t *testing.T) {
 	switch runtime.GOOS {
-	case "js", "nacl", "plan9", "windows":
+	case "aix", "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
 	if !supportsIPv6 {
@@ -73,6 +73,8 @@
 }
 
 func testMulticastSocketOptions(t *testing.T, c testIPv6MulticastConn, ifi *net.Interface, grp net.Addr) {
+	t.Helper()
+
 	const hoplim = 255
 	if err := c.SetMulticastHopLimit(hoplim); err != nil {
 		t.Error(err)
@@ -111,6 +113,8 @@
 }
 
 func testSourceSpecificMulticastSocketOptions(t *testing.T, c testIPv6MulticastConn, ifi *net.Interface, grp, src net.Addr) {
+	t.Helper()
+
 	// MCAST_JOIN_GROUP -> MCAST_BLOCK_SOURCE -> MCAST_UNBLOCK_SOURCE -> MCAST_LEAVE_GROUP
 	if err := c.JoinGroup(ifi, grp); err != nil {
 		t.Error(err)