RFR: 8376290: SocketChannel.finishConnect() contains confusing "getsockopt" in exception message for a failed connect() on Windows

[Jaikiran Pai]

Can I please get a review of this change which proposes to remove the confusing "getsockopt" text from the exception reported on Windows when `SocketChannel.finishConnect()` raises an exception due to a failed `connect()`? 

This addresses https://bugs.openjdk.org/browse/JDK-8376290 and as noted in that issue, this looks like an oversight when changes were done for https://bugs.openjdk.org/browse/JDK-8317603. Prior to that, on older versions the exception reported on Windows was:


java.net.ConnectException: Connection refused: no further information


With the current proposed changes in this PR, the exception will now be `java.net.ConnectException: Connection refused` which matches what we report on *nix platforms.

A new jtreg test has been added to reproduce the original text and verify the change. tier1, tier2 and tier3 continue to pass with this change.

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Commit messages:
 - add bug id to the test
 - allow NULL for msg in NET_ThrowNew
 - introduce test

Changes: https://git.openjdk.org/jdk/pull/29409/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29409&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376290
  Stats: 157 lines in 4 files changed: 135 ins; 10 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/29409.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29409/head:pull/29409

PR: https://git.openjdk.org/jdk/pull/29409