RFR: 8310807: java/nio/channels/DatagramChannel/Connect.java timed out

[Daniel Fuchs]

Please find here a fix for a timeout issue observed in DatagramChannel/Connect.java

The suspicion is that the responder may have received some message from some other source and replied to that, leaving the initiator waiting forever.

The proposed fix makes sure the messages exchanged are unique and identifiable and ensure that both the initiator and responder will discard any message that do not have the expected content.

Additional logging should help with diagnosis if the test fails again.

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Commit messages:
 - Minor cleanup 2
 - Minor cleanup
 - 8310807

Changes: https://git.openjdk.org/jdk/pull/16661/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16661&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310807
  Stats: 80 lines in 1 file changed: 42 ins; 0 del; 38 mod
  Patch: https://git.openjdk.org/jdk/pull/16661.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16661/head:pull/16661

PR: https://git.openjdk.org/jdk/pull/16661