RFR: 8335771: Improve stability of java/nio/channels/DatagramChannel tests [v4]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' into JDK-8335771
 - Review feedback
 - Review feedback: avoid continue
 - Review feedback
 - 8335771

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/20050/files
  - new: https://git.openjdk.org/jdk/pull/20050/files/64fccfb6..14c607fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20050&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20050&range=02-03

  Stats: 45890 lines in 1489 files changed: 25205 ins; 14342 del; 6343 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