Improve the hash algorithm for QUIC connection table

QUIC connection table is a hash table and the key is a QUIC connection ID. Because the initial ID for a connection is generated on the client side, it is possible to cause hash collisions intentionally. The hash algorithm needs to be improved.

We don't have a CVE number for this because our QUIC implementation is still experimental. We need to address this before we call our QUIC support production-ready.