nginx: fix debug log when SCID length is mismatched
nginx: fix debug log when SCID length is mismatched

Debug lines for new QUIC connections print the server's
SCID. Previously, we mistakenly used the length the client SCID
which could cause some incorrectness. For example, Chrome sends
a 0-length SCID.

This change ensures we use the actual server SCID length.
cloudflare/quiche,cloudflare/quiche,cloudflare/quiche