RFR: 8277957: Add test group for IPv6 exclusive testing [v2]

[Dermot Boyle]

On Fri, 3 Dec 2021 20:26:46 GMT, Ivan Šipka <isipka at openjdk.org> wrote:

>> Adding test group for IPv6 exclusive testing.
>
> Ivan Šipka has updated the pull request incrementally with one additional commit since the last revision:
> 
>   added comment for adding the ipv6_only  testgroup

Marked as reviewed by dermotb at github.com (no known OpenJDK username).

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PR: https://git.openjdk.java.net/jdk/pull/6600