MINOR: h3: Add the quic_conn object to h3 traces

This is very useful to associate h3 traces to a QUIC connection when debugging.

Must be backported to 2.6.
diff --git a/src/h3.c b/src/h3.c
index 28656fc..f1cf4e1 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -1253,6 +1253,8 @@
 
 	if (src->verbosity > H3_VERB_CLEAN) {
 		chunk_appendf(&trace_buf, " : qcc=%p(F)", qcc);
+		if (qcc->conn->handle.qc)
+			chunk_appendf(&trace_buf, " qc=%p", qcc->conn->handle.qc);
 
 		if (qcs)
 			chunk_appendf(&trace_buf, " qcs=%p(%llu)", qcs, (ull)qcs->id);