RFR: 8254692: (se) Clarify the behaviour of the non-abstract SelectorProvider::inheritedChannel

[Fernando Guallini]

Please review this fix to provide spec clarity on the default implementation of
java.nio.channels.spi.SelectorProvider::inheritedChannel() method which simply returns “null”, and a test for it.

Please review the corresponding CSR as well: https://bugs.openjdk.java.net/browse/JDK-8254848

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

Commit messages:
 - add bug number to ProtocolFamilies test
 - add implSpec to SelectorProvider::inheritedChannel and tests for method default behaviour

Changes: https://git.openjdk.java.net/jdk/pull/745/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=745&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254692
  Stats: 9 lines in 2 files changed: 7 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/745.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/745/head:pull/745

PR: https://git.openjdk.java.net/jdk/pull/745