http2: rename function for clarity

The function does not only validate the input but it causes side
effects by adding default options to the input object in case the
option is not set.

PR-URL: https://github.com/nodejs/node/pull/26809


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>