[jdk11u-dev] RFR: 8233989: Create an IPv4 version of java/net/MulticastSocket/SetLoopbackMode.java

[Zhengyu Gu]

I would like to backport this patch to openjdk11u for parity with Oracle 11.0.13.

The original patch applies cleanly.

Test:
- [x]  java/net/MulticastSocket/SetLoopbackMode.java
- [x]  java/net/MulticastSocket/SetLoopbackModeIPv4.java

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Commit messages:
 - Backport 78accb56022aab9c013d7abb7187ebbd0c0d915a

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/54/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=54&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8233989
  Stats: 46 lines in 2 files changed: 45 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/54.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/54/head:pull/54

PR: https://git.openjdk.java.net/jdk11u-dev/pull/54