[jdk11u-dev] RFR: 8229348: java/net/DatagramSocket/UnreferencedDatagramSockets.java fails intermittently

[luchenlin]

I backport this for parity with 11.0.20-oracle.

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Commit messages:
 - Backport 6d63995ada6b4f2cdd8921dc254276fe724a12c4

Changes: https://git.openjdk.org/jdk11u-dev/pull/1922/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1922&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8229348
  Stats: 13 lines in 1 file changed: 8 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1922.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/1922/head:pull/1922

PR: https://git.openjdk.org/jdk11u-dev/pull/1922