RFR: 8269481: SctpMultiChannel never releases own file descriptor

[Brian Burkhalter]

Please review this change to the Unix implementations of `sun.nio.ch.sctp.Sctp*ChannelImpl#kill()` to close the socket if `state == ChannelState.UNINITIALIZED`.

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Commit messages:
 - 8269481: SctpMultiChannel never releases own file descriptor

Changes: https://git.openjdk.java.net/jdk/pull/4621/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4621&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269481
  Stats: 128 lines in 4 files changed: 128 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4621.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4621/head:pull/4621

PR: https://git.openjdk.java.net/jdk/pull/4621