RFR: 8286763: [REDO] (fc) Tune FileChannel.transferFrom()

[Brian Burkhalter]

Re-do the fix for [JDK-8274113](https://bugs.openjdk.java.net/browse/JDK-8274113) which was reverted by [JDK-8286677.](https://bugs.openjdk.java.net/browse/JDK-8286677)

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Commit messages:
 - 8286763: [REDO] (fc) Tune FileChannel.transferFrom()

Changes: https://git.openjdk.java.net/jdk/pull/8733/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8733&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286763
  Stats: 131 lines in 4 files changed: 117 ins; 0 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8733.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8733/head:pull/8733

PR: https://git.openjdk.java.net/jdk/pull/8733