6965072: update SDP support

[Alan Bateman]

Michael - do you mind reviewing this one?

This is a change to the SDP support to make it easy to provide an API in 
the future.  For now it includes a simple implementation specific API. 
The existing transparent support continues to work but is reorganized to 
allow for both transparent and API usage. The webrev with the changes is 
here:
   http://cr.openjdk.java.net/~alanb/6965072/webrev/

Thanks,
Alan.