MINOR: quic: handle CONNECTION_CLOSE frame

On receiving CONNECTION_CLOSE frame, the mux is flagged for immediate
connection close. A stream is closed even if there is data not ACKed
left if CONNECTION_CLOSE has been received.

include/haproxy/mux_quic-t.h

@@ -77,6 +77,8 @@
 /* other flags */
 #define QC_CF_IS_BACK           0x00008000  // this is an outgoing connection
 
+#define QC_CF_CC_RECV           0x00010000  // CONNECTION_CLOSE received
+
 extern struct pool_head *pool_head_qcs;
 
 /* Stream types */