RFR: 8343442: Add since checker tests to the networking area modules

[Nizar Benalla]

Can I please get a review for this patch that brings the `@since` test described [here](https://mail.openjdk.org/pipermail/jdk-dev/2024-October/009474.html) to the networking area modules.

The benefit from this is helping API authors and reviewer validate the accuracy of `@since` in their source code (and subsequently, in the generated documentation).

The test has been added for `java.base` 2 weeks ago and has helped catch some bugs before they make it to the JDK.

TIA

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Commit messages:
 - This file should not have been changed
 - add a test for since tags in the source to the networking area modules

Changes: https://git.openjdk.org/jdk/pull/21838/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21838&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343442
  Stats: 8 lines in 3 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/21838.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21838/head:pull/21838

PR: https://git.openjdk.org/jdk/pull/21838