8032451: (dc) DatagramChannel.join should support include-mode filtering on OS X

[Alan Bateman]

This is another OS X specific issue (again going back original port 
where there were a number of things left out).

DatagramChannel has API support for source-specific multicasting but it 
has always been disabled on OS X (this is allowed by the spec). Part of 
the issue seems to be the definition of ip_mreq_source that came from 
the BSD porting project and doesn't seem to match the header files on OS 
X. With this removed (meaning using the definitions from the system 
header files) then include-mode filtering with IPv4 works and the tests 
pass on 10.7, 10.8 and 10.9. There are still problems with IPv6 
source-specific multicasting where it's not completely clear what each 
OS X release supports. So for now I would like to enable include-mode 
filtering for IPv4 with the following changes:

http://cr.openjdk.java.net/~alanb/8032451/webrev/

-Alan.