[jdk21u-dev] RFR: 8327370: (ch) sun.nio.ch.Poller.register throws AssertionError

[Satyen Subramaniam]

Backporting JDK-8327370: (ch) sun.nio.ch.Poller.register throws AssertionError. Fixes an intermittent AssertionError observed in sun.nio.ch.Poller. Ran GHA Sanity Checks, local Tier 1 and 2 tests. Patch is clean.

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Commit messages:
 - Backport d2bebffb1fd26fae4526afd33a818ee776b7102e

Changes: https://git.openjdk.org/jdk21u-dev/pull/1617/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1617&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327370
  Stats: 7 lines in 1 file changed: 5 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1617.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1617/head:pull/1617

PR: https://git.openjdk.org/jdk21u-dev/pull/1617