MEDIUM: quic: trigger fast connection closing on process stopping

MEDIUM: quic: trigger fast connection closing on process stopping

With previous commit, quic-conn are now handled as jobs to prevent the
termination of haproxy process. This ensures that QUIC connections are
closed when all data are acknowledged by the client and there is no more
active streams.

The quic-conn layer emits a CONNECTION_CLOSE once the MUX has been
released and all streams are acknowledged. Then, the timer is scheduled
to definitely free the connection after the idle timeout period. This
allows to treat late-arriving packets.

Adjust this procedure to deactivate this timer when process stopping is
in progress. In this case, quic-conn timer is set to expire immediately
to free the quic-conn instance as soon as possible. This allows to
quickly close haproxy process.

This should be backported up to 2.7.