test: add minimal test for net benchmarks

Currently, benchmark code is not exercised at all in CI. This adds a
minimal test for net benchmarks. If this is deemed acceptable, similar
minimal tests for other benchmarks can be written. Additionally, as
issues and edge cases are uncovered, checks for them can be added.

PR-URL: https://github.com/nodejs/node/pull/11979


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>