test: add http_incoming's matchKnownFields test

https://github.com/nodejs/node/blob/master/lib/_http_incoming.js#L136
Coverage: https://coverage.nodejs.org/coverage-57f6a106fbc69a47/root/_http_incoming.js.html

PR-URL: https://github.com/nodejs/node/pull/10811


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>