RFR: 8285646: Add test that checks IP_DONTFRAGMENT is a supported option

[Michael McMahon]

Hi,

Could I get the following small test update reviewed please?
It includes a test scenario that should have been included with JDK-8284890

Thanks,
Michael

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Commit messages:
 - test update

Changes: https://git.openjdk.java.net/jdk/pull/8405/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8405&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285646
  Stats: 9 lines in 1 file changed: 9 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8405.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8405/head:pull/8405

PR: https://git.openjdk.java.net/jdk/pull/8405