RFR: 8335771: Improve stability of java/nio/channels/DatagramChannel tests [v3]

[Daniel Fuchs]

> Several `java/nio/channels/DatagramChannel` tests fail intermittently. Though it seems difficult to fix all intermittent failures due to the nature of what some of these attempt to test, the stability can still be improved.
> 
> The most common source of intermittent failures are:
> 
>  - not receiving a datagram due to port conflict or interference of concurrent running tests
>  - failure to disconnect due to interference of concurrent running tests
>  - failure due to reception of unexpected stray datagrams
> 
> Avoiding to bind on the wildcard address, filtering unexpected datagram, and some retrying can aleviate some of the issues and greatly reduce the frequency of intermittent failures.

Daniel Fuchs has updated the pull request incrementally with one additional commit since the last revision:

  Review feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20050/files
  - new: https://git.openjdk.org/jdk/pull/20050/files/6695360d..64fccfb6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20050&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20050&range=01-02

  Stats: 18 lines in 3 files changed: 7 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/20050.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20050/head:pull/20050

PR: https://git.openjdk.org/jdk/pull/20050