RFR: 8365983: Tests should throw SkippedException when SCTP not supported

[SendaoYan]

Currently, take test/jdk/com/sun/nio/sctp/SctpMultiChannel/Branch.java as example. When Util.isSCTPSupported() return false, then test print a warning and the exit.

I think it's better to throw jtreg.SkippedException rather than only print a warning and then report test passed.

Change has been verified locally, test-fix only, almost no risk.

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

Commit messages:
 - 8365983: Tests should throw SkippedException when SCTP not supported

Changes: https://git.openjdk.org/jdk/pull/26903/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26903&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365983
  Stats: 207 lines in 15 files changed: 101 ins; 89 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/26903.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26903/head:pull/26903

PR: https://git.openjdk.org/jdk/pull/26903