test: allow out-of-order replies in dgram tests

Allow out of order replies in the flaky
`test-dgram{-upd6,}-send-default-host.js` files by sorting
the incoming replies after receiving them.

PR-URL: https://github.com/nodejs/node/pull/6607
Fixes: https://github.com/nodejs/node/issues/6577


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>