Jetty server high CPU when client send data length > 17408

This affects SSL connections only, which is not part of our default setup.
Adapted from workaround at:
https://github.com/eclipse/jetty.project/security/advisories/GHSA-26vr-8j45-3r4w
Put the new checks directly in the unwrap() method,
rather than subclassing SslConnection, as that would require config file changes.