RFR: 8309302: java/net/Socket/Timeouts.java fails with AssertionError on test temporal post condition

[Darragh Clarke]

Bumped timeout limit to `+20_000` to deal with occasional failure and bring the test in line with other tests like [SleepWithDuration](https://github.com/openjdk/jdk/blob/c3f10e847999ec254893de5a1a5de32fd07f715a/test/jdk/java/lang/Thread/SleepWithDuration.java#L46) and [JoinWithDuration](https://github.com/openjdk/jdk/blob/c3f10e847999ec254893de5a1a5de32fd07f715a/test/jdk/java/lang/Thread/JoinWithDuration.java#L67) .

I had considered making a Util class to contain `checkDuration` but decided against it because as far as I'm aware it is only these 3 classes that would share it, though I would be open to adding it if people think it adds value

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Commit messages:
 - increased timeouts from +2000 to +20_000

Changes: https://git.openjdk.org/jdk/pull/14690/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14690&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309302
  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/14690.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14690/head:pull/14690

PR: https://git.openjdk.org/jdk/pull/14690