Flaky case test_dgram_multicast_set_multicast_loop.js

[legendecas]

Seems there is an error:

AssertionError: {"actual":1,"expected":0,"operator":"==="}
    at AssertionError (/Users/travis/build/yodaos-project/ShadowNode/src/js/assert.js.wrapped:42:1)
    at fail (/Users/travis/build/yodaos-project/ShadowNode/src/js/assert.js.wrapped:69:1)
    at strictEqual (/Users/travis/build/yodaos-project/ShadowNode/src/js/assert.js.wrapped:95:1)
    at undefined (/Users/travis/build/yodaos-project/ShadowNode/test/run_pass/test_dgram_multicast_set_multicast_loop.js:44:20)
    at undefined (/Users/travis/build/yodaos-project/ShadowNode/src/js/events.js.wrapped:57:31)
    at undefined (/Users/travis/build/yodaos-project/ShadowNode/src/js/iotjs.js.wrapped:446:22)
    at undefined (/Users/travis/build/yodaos-project/ShadowNode/src/js/iotjs.js.wrapped:491:18)
    at _onUncaughtException (/Users/travis/build/yodaos-project/ShadowNode/src/js/iotjs.js.wrapped:68:3)

Originally posted by @yorkie in #527 (comment)