Disable Multicast Loopback test for Linux IPv6, temporarily

tests/standalone/io/raw_datagram_socket_test.dart

Index: tests/standalone/io/raw_datagram_socket_test.dart
diff --git a/tests/standalone/io/raw_datagram_socket_test.dart b/tests/standalone/io/raw_datagram_socket_test.dart
index 996a83f7910d6dfbec60df3e42aea8bf6af8455e..2a08b0cde37e53fec7a64243af6a647d0441fc09 100644
--- a/tests/standalone/io/raw_datagram_socket_test.dart
+++ b/tests/standalone/io/raw_datagram_socket_test.dart
@@ -192,7 +192,8 @@ testLoopbackMulticast() {
 
   test(InternetAddress.ANY_IP_V4, new InternetAddress("228.0.0.4"), true);
   test(InternetAddress.ANY_IP_V4, new InternetAddress("224.0.0.0"), false);
-  if (!Platform.isMacOS) {
+  // TODO(30306): Reenable for Linux
+  if (!Platform.isMacOS && !Platform.isLinux) {
     test(InternetAddress.ANY_IP_V6, new InternetAddress("ff11::0"), true);
     test(InternetAddress.ANY_IP_V6, new InternetAddress("ff11::0"), false);
   }