test: refactor pummel/test-net-connect-econnrefused

* Reduce ROUNDS and ATTEMPTS_PER_ROUND by half to avoid spurious test
  failures as a result of side effects from other tests. (For my local
  setup, test-keep-alive seems to cause this test to fail with ETIMEDOUT
  and/or EADDRNOTAVAIL. It would seem to be a result of throttling.
  Reducing the pummel-iness of that test and this one seems to solve the
  problem.)
* Apply capitalization and punctuation to comment.

PR-URL: https://github.com/nodejs/node/pull/25485


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>