http2: allow security revert for Ping/Settings Flood

nghttp2 has updated its limit for outstanding Ping/Settings ACKs
to 1000. This commit allows reverting to the old default of 10000.

The associated CVEs are CVE-2019-9512/CVE-2019-9515.

Backport-PR-URL: https://github.com/nodejs/node/pull/29124
PR-URL: https://github.com/nodejs/node/pull/29122


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>