Disable the ping6 flowlabel test, since it doesn't work.

This has never worked on any released kernel. I committed it when
I had local changes that made it work, but those changes were not
accepted upstream.

Change-Id: Ie6e356414551744c1c4ed7c1572fe0228a5db8db
diff --git a/net/test/ping6_test.py b/net/test/ping6_test.py
index ff680b8..57365ae 100755
--- a/net/test/ping6_test.py
+++ b/net/test/ping6_test.py
@@ -377,7 +377,7 @@
     self.assertRaisesErrno(errno.EINVAL, s.sendto, net_test.IPV6_PING,
                            ("::ffff:", 55))
-  @unittest.skipUnless(net_test.HAVE_IPV6, "skipping: no IPv6")
+  @unittest.skipUnless(False, "skipping: does not work yet")
   def testFlowLabel(self):
     s = net_test.IPv6PingSocket()