[jdk17u-dev] RFR: 8308593: Add KEEPALIVE Extended Socket Options Support for Windows [v2]

[Terry Chow]

> This is an unclean backport of [JDK-8308593](https://bugs.openjdk.org/browse/JDK-8308593), which provides support for the keepalive extended socket options on Windows.
> 
> The following changes were made in these files to resolve conflicts and issues:
> 1. make/modules/jdk.net/Lib.gmk -- I updated this script to support building extnet for Windows.
> 
> 2. jdk.net/share/classes/jdk/net/ExtendedSocketOptions.java -- I added a case to support returning an instance of WindowsSocketOptions in PlatformSocketOptions.
> 
> 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.

Terry Chow has updated the pull request incrementally with one additional commit since the last revision:

  Code review -- updated copyright lines

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

Changes:
  - all: https://git.openjdk.org/jdk17u-dev/pull/1751/files
  - new: https://git.openjdk.org/jdk17u-dev/pull/1751/files/7c75b9dd..9925cf21

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1751&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1751&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1751.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1751/head:pull/1751

PR: https://git.openjdk.org/jdk17u-dev/pull/1751