fix the crypto setup so that it works with the recent mint changes
fix the crypto setup so that it works with the recent mint changes

mint now supports stateless retries, and requires that the cookie
protector is set in the mint.Config and returns a new alert when a
retry is performed.

konnykonny50/quic-go,konnykonny50/quic-go,lucas-clemente/quic-go,lucas-clemente/quic-go