RFR: JDK-8315318: Typo in comment on sun.nio.ch.Net.unblock4

[shiker]

Modify the comment on the unblock4() method, because the original comment will cause people to misunderstand.

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Commit messages:
 - Update Net.java

Changes: https://git.openjdk.org/jdk/pull/15186/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15186&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315318
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15186.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15186/head:pull/15186

PR: https://git.openjdk.org/jdk/pull/15186