MINOR: mux-quic: use send-list for STOP_SENDING/RESET_STREAM emission

MINOR: mux-quic: use send-list for STOP_SENDING/RESET_STREAM emission

When a STOP_SENDING or RESET_STREAM must be send, its corresponding qcs
is inserted into <qcc.send_list> via qcc_reset_stream() or
qcc_abort_stream_read().

This allows to remove the iteration on full qcs tree in qc_send().
Instead, STOP_SENDING and RESET_STREAM is done in the loop over
<qcc.send_list> as with STREAM frames. This should improve slightly the
performance, most notably when large number of streams are opened.

This must be backported up to 2.7.