RFR: JDK-8273246 Amend the test java/nio/channels/DatagramChannel/ManySourcesAndTargets.java to execute in othervm mode [v2]

[Mark Sheppard]

> A number of nio DatagramChannel tests are intermittently failing on macosx-aarch64.
> In some instances this is a receive call blocking indefinitely waiting on data which has
> already been sent, and should be available immediately to the receive method call.
> Other test failure scenarios are problems during the test compilation phase with a SocketException being thrown and the message:
> "test result: Error. Agent communication error: java.net.SocketException: No buffer space available; check console log for any additional details"
> 
> The ManySourcesAndTargets and other tests execute in agentvm mode. This results in certain test diagnostic
> Output being lost during the test failure handling capture process. To mitigate this lost diagnostics, the
> ManySourcesAndTargets test has been amended to execute in othervm mode.
> 
> Additionally, to assist in the buffer allocation issue, the netstat command executed by the test
> failure_handler has an extra argument added to obtain additional details on mbuf usage.
> The failure handler will now execute with netstat -mm

Mark Sheppard has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8273246 fix logic error in testReceive method change reader.send to sender.send

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5366/files
  - new: https://git.openjdk.java.net/jdk/pull/5366/files/afe29d42..0effbcd4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5366&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5366&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5366.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5366/head:pull/5366

PR: https://git.openjdk.java.net/jdk/pull/5366