[jdk21u] RFR: 8308593: Add KEEPALIVE Extended Socket Options Support for Windows

Tue Aug 29 17:15:22 UTC 2023

This is a clean backport of [JDK-8308593](https://bugs.openjdk.org/browse/JDK-8308593), which provides support for the keepalive extended socket options on Windows.

Tier 1 tests were ran and they're passing along with the existing keepalive tests. I also manually tested and confirmed the patch to be working on Windows (specifically Windows 10 since that's the only Windows platform available to me at the moment).

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Commit messages:
 - Backport f3ade388dac0b882e671462caa762138f44817fb

Changes: https://git.openjdk.org/jdk21u/pull/117/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=117&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308593
  Stats: 210 lines in 9 files changed: 169 ins; 0 del; 41 mod
  Patch: https://git.openjdk.org/jdk21u/pull/117.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/117/head:pull/117

PR: https://git.openjdk.org/jdk21u/pull/117