Fix ossl_quic_trace to fetch connection short conn id len

Fix ossl_quic_trace to fetch connection short conn id len

ossl_quic_trace currently fails to get the connection id when parsing a
short header.  now that we have an api to get the known length, go ahead
and use that to parse the header properly

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26592)