MINOR: mux-quic: close connection asap on local error

MINOR: mux-quic: close connection asap on local error

With the change for QUIC MUX local error API, the new flag QC_CF_ERRL is
now checked on qc_detach(). If set, qcs instance is freed even though
transfer is not finished. This should help to quickly release qcs and
eventually all MUX instance resources.

To further accelerate this, a specific check has been added in
qc_shutw(). It is skipped if local error flag is set to prevent noisy
reset stream invocation. In the same way, QUIC MUX is not rescheduled on
qc_recv_buf() operation if local error flag set.

This should be backported up to 2.7.