MINOR: mux-quic: do not consider CONNECTION_CLOSE for the moment

MINOR: mux-quic: do not consider CONNECTION_CLOSE for the moment

Remove the condition on CONNECTION_CLOSE reception to close immediately
streams. It can cause some crash as the QUIC xprt layer still access the
qcs to send data and handle ACK.

The whole interface and buffering between QUIC xprt and mux must be
properly reorganized to better handle this case. Once this is done, it
may have some sense to free the qcs streams on CONNECTION_CLOSE
reception.