MINOR: quic: use the right trace event in quic_tls_key_update()

MINOR: quic: use the right trace event in quic_tls_key_update()

The next RX/TX secret lengths are reported with QUIC_EV_CONN_SPPKTS,
whose handler expects a <struct quic_tx_packet *>, while the rest of the
function uses QUIC_EV_CONN_KP event. TRACE_PRINTF() bypasses the source
callback through <&trace_no_cb>, so nothing crashed: the message was
just filtered under the wrong event.