7161881: (dc) DatagramChannel.bind(null) fails if IPv4 socket and running with preferIPv6Addresses=true

[Rob McKenna]

Hi folks,

Small bug with in DatagramChannel where 
Java.net.preferIPv6Addresses=true is causing bind(null) to use an ipv6 
address even though we're connected to an ipv4 socket.

Additional context:
http://mail.openjdk.java.net/pipermail/nio-dev/2012-April/001632.html

Webrev:
http://cr.openjdk.java.net/~robm/7161881/webrev.01/

     -Rob