flaky test-dgram-multicast-ssmv6-multi-process on linux

[sam-github]

examples of failure from the last weeks masters:

• https://ci.nodejs.org/job/node-test-commit-custom-suites-freestyle/13723/
• https://ci.nodejs.org/job/node-test-commit-custom-suites-freestyle/13706/
• https://ci.nodejs.org/job/node-test-commit-custom-suites-freestyle/13640/
• https://ci.nodejs.org/job/node-test-commit-custom-suites-freestyle/13516/

Error Message
[PARENT] sent "First message to send" to ff3e::1234:15000
[PARENT] sent "Second message to send" to ff3e::1234:15000
[PARENT] sent "Third message to send" to ff3e::1234:15000
[PARENT] sent "Fourth message to send" to ff3e::1234:15000
[PARENT] sendSocket closed
[PARENT] Responses were not received within 5000 ms.
[PARENT] Fail
assert.js:142
  throw err;
  ^

AssertionError [ERR_ASSERTION]: Failed
    at Timeout._onTimeout (/home/iojs/build/workspace/node-test-commit-custom-suites-freestyle/test/internet/test-dgram-multicast-ssmv6-multi-process.js:140:12)
    at listOnTimeout (internal/timers.js:549:17)
    at processTimers (internal/timers.js:492:7) {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: undefined,
  expected: undefined,
  operator: 'fail'
}

[sam-github]

still failing: https://ci.nodejs.org/job/node-test-commit-custom-suites-freestyle/14334/

[Trott]

Because these problems can sometimes be host-specific: The host this is failing on is test-rackspace-ubuntu1604-x64-2

[richardlau]

Happened in https://ci.nodejs.org/job/node-test-commit-custom-suites-freestyle/25610/ (from today's daily build) on test-ibm-ubuntu1804-x64-2.

[Trott]

Same/similar to nodejs/build#2165?