RFR: 8297778: Modernize and improve module jdk.sctp

[Per Minborg]

This PR proposes a variety of modernisations to the `jdk.sctp` module.

During the fix of https://bugs.openjdk.org/browse/JDK-8296024, several improvement areas were identified including: 

* Replacing duplicate code segments 
* Making certain fields final 
* Using enhanced switch 
* Using records 
* Fixing typos 
* Marking fields participating in serialisation with `@Serial` 
* Modernizing toString() implementations 
* Using pattern matching 
* Using diamond operators

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Commit messages:
 - Modernize module jdk.sctp

Changes: https://git.openjdk.org/jdk/pull/11418/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11418&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297778
  Stats: 609 lines in 31 files changed: 102 ins; 176 del; 331 mod
  Patch: https://git.openjdk.org/jdk/pull/11418.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11418/head:pull/11418

PR: https://git.openjdk.org/jdk/pull/11418