http: fix _dump regression

A recent set of changes removed _consuming tracking from server
incoming messages which ensures that _dump only runs if the
user has never attempted to read the incoming data. Fix by
reintroducing _consuming which tracks whether _read was ever
successfully called.

PR-URL: https://github.com/nodejs/node/pull/20088


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>