RFR: JDK-8314517: some tests fail in case ipv6 is disabled on the machine

[Matthias Baesken]

Some jtreg tests fail with ipv6 disabled on the machine, this should be improved in the tests (e.g. by using IPSupport.hasIPv6() ).

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Commit messages:
 - JDK-8314517

Changes: https://git.openjdk.org/jdk/pull/15341/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15341&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314517
  Stats: 90 lines in 6 files changed: 33 ins; 1 del; 56 mod
  Patch: https://git.openjdk.org/jdk/pull/15341.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15341/head:pull/15341

PR: https://git.openjdk.org/jdk/pull/15341