[jdk21u-dev] RFR: 8339787: Add some additional diagnostic output to java/net/ipv6tests/UdpTest.java

[Goetz Lindenmaier]

I backport this for parity with 21.0.6-oracle.

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Commit messages:
 - Backport cecb0b3d11ed0ce204cb6c3427f5a6858a844aeb

Changes: https://git.openjdk.org/jdk21u-dev/pull/1081/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1081&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339787
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1081.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1081/head:pull/1081

PR: https://git.openjdk.org/jdk21u-dev/pull/1081