RFR: 8356395: Spec needs to be clarified for InterfaceAddress.getBroadcast() method

[kieran-farrell]

Spec currently suggests that only IPv6 addresses can return null for InterfaceAddress.getBroadcast(). Clarifying spec to state that certain IPv4 address such as the loopback address do not support broadcasting and can therefore also return null.

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Commit messages:
 - update inetaddress javadoc

Changes: https://git.openjdk.org/jdk/pull/25095/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25095&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356395
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25095.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25095/head:pull/25095

PR: https://git.openjdk.org/jdk/pull/25095