Track received data correctly. Specifically, for the buffer that
is used for receiving data, we previously would try to increment
the current memory usage by its length, and later decrement it
by that, but in the meantime the buffer had been turned over to V8
and its length reset to zero. This gave the impression that more and
more memory was consumed by the HTTP/2 session when it was in fact not.
Fixes: https://github.com/nodejs/node/issues/27416
Refs: https://github.com/nodejs/node/pull/26207
PR-URL: https://github.com/nodejs/node/pull/27914
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>