=doc #15772 Make IPv6 multicast tests work on OS X

* Fixed a small race by waiting for the listenert to be bound
* Changed the Java test to test the Java code (imported the wrong class)
* Changed to a known link local multicas address (the old one just gave me a no route to host)
some comment here explaining how this is a "known address"? (I wouldn't recognise it is, as is).