JDK-8148424 Support IPv6-only Unix environments

[Chris Hegarty]

Martin,

Promoted by some other changes that are going on, I stumbled
across your proposal for 8148424: "Support IPv6-only Unix
environments” [1][2][3].

I think the changes are good. I rebased them against the latest
source in jdk9/dev.

  http://cr.openjdk.java.net/~chegar/8148424/

I put the changes through our build and test system, and there
are no surprising results.  Have you done much testing of the 
change in your environment?

-Chris

[1] http://mail.openjdk.java.net/pipermail/nio-dev/2016-January/003509.html
[2] http://cr.openjdk.java.net/~martin/webrevs/openjdk9/ipv6-only/
[3] https://bugs.openjdk.java.net/browse/JDK-8148424