RFR: 8297778: Modernize and improve module jdk.sctp [v6]

[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

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Add import and remove redundant assignments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11418/files
  - new: https://git.openjdk.org/jdk/pull/11418/files/8cbc6edd..bfef4462

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11418&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11418&range=04-05

  Stats: 4 lines in 2 files changed: 1 ins; 0 del; 3 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