QUIC: attempt decrypt before checking for stateless reset.

QUIC: attempt decrypt before checking for stateless reset.

Checking the reset after encryption avoids false positives.  More importantly,
it avoids the check entirely in the usual case where decryption succeeds.

RFC 9000, 10.3.1  Detecting a Stateless Reset

    Endpoints MAY skip this check if any packet from a datagram is
    successfully processed.