http2: implement support for max settings entries

Adds the maxSettings option to limit the number of settings
entries allowed per SETTINGS frame. Default 32

Signed-off-by: James M Snell <jasnell@gmail.com>

Fixes: https://hackerone.com/reports/446662
CVE-ID: CVE-2020-11080
PR-URL: https://github.com/nodejs-private/node-private/pull/204
Backport-PR-URL: https://github.com/nodejs-private/node-private/pull/207


Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>