RFR: 8262883: doccheck: Broken links in java.base

[Michael McMahon]

Hi,

Could I get the following trivial doc changes reviewed please, caused by:

- broken <A> tags in MethodHandles referring to package.html instead of package-summary.html

- references to a package level #unixdomain anchor that no longer exists.

- a <a> tag missing a "../" in SocketChannel

Thanks,

Michael

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Commit messages:
 - Fixed SocketChannel
 - fixed links in apidoc

Changes: https://git.openjdk.java.net/jdk/pull/3491/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3491&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262883
  Stats: 5 lines in 4 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3491.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3491/head:pull/3491

PR: https://git.openjdk.java.net/jdk/pull/3491