MINOR: quic: Send CONNECTION_CLOSE frame upon TLS alert

Add ->err member to quic_conn struct to store the connection errors.
This is the responsability of ->send_alert callback of SSL_QUIC_METHOD
struct to handle the TLS alert and consequently update ->err value.
At this time, when entering qc_build_pkt() we build a CONNECTION_CLOSE
frame close the connection when ->err value is not null.
2 files changed