RFR: 8373704: Improve "SocketException: Protocol family unavailable" message

[Matthias Baesken]

In [JDK-8373676](https://bugs.openjdk.org/browse/JDK-8373676)
we noticed a "SocketException: Protocol family unavailable" because of missing ipv6 support. We could improve this exception and tell that the ipv6 support is not available or something related.

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Commit messages:
 - JDK-8373704

Changes: https://git.openjdk.org/jdk/pull/28851/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28851&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373704
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28851.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28851/head:pull/28851

PR: https://git.openjdk.org/jdk/pull/28851