BUG/MINOR: h3: fix crash due to h3 traces

First H3 traces argument must be a connection instance or a NULL. Some
new traces were added recently with a qcc instance which caused a crash
when traces are activated.

This trace was added by the following patch :
    87f8766d3fbd10f9e8bf4902d37712612db64df5
    BUG/MEDIUM: h3: handle STOP_SENDING on control stream

This must be backported up to 2.6 along with the above patch.
diff --git a/src/h3.c b/src/h3.c
index 07a7e7c..d625807 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -1629,7 +1629,7 @@
 	 * as a connection error of type H3_CLOSED_CRITICAL_STREAM.
 	 */
 	if (qcs == h3c->ctrl_strm || h3s->type == H3S_T_CTRL) {
-		TRACE_ERROR("closure detected on control stream", H3_EV_H3S_END, qcs->qcc, qcs);
+		TRACE_ERROR("closure detected on control stream", H3_EV_H3S_END, qcs->qcc->conn, qcs);
 		qcc_emit_cc_app(qcs->qcc, H3_CLOSED_CRITICAL_STREAM, 1);
 		return 1;
 	}