Revert "MINOR: quic: Remove useless traces about references to TX packets"

This reverts commit f61398a7caa35d780639a5961d2b1ea427f710b6.
After having checked a version with more traces and reproduced the issue
as reported by Tristan in GH #1808, there are remaining cases where
a duplicated but not already sent frame have to be marked as acked because
the frame it was copied from was acknowledeged before its copied was sent.

Must be backported to 2.6.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index 30af64e..0aad272 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -1475,8 +1475,14 @@
 	list_for_each_entry_safe(f, tmp, &frm->reflist, ref) {
 		f->origin = NULL;
 		LIST_DELETE(&f->ref);
-		TRACE_DEVEL("remove frame reference",
-		            QUIC_EV_CONN_PRSAFRM, qc, f, &f->pkt->pn_node.key);
+		if (f->pkt) {
+			TRACE_DEVEL("remove frame reference",
+			            QUIC_EV_CONN_PRSAFRM, qc, f, &f->pkt->pn_node.key);
+		}
+		else {
+			TRACE_DEVEL("remove frame reference for unsent frame",
+			            QUIC_EV_CONN_PRSAFRM, qc, f);
+		}
 	}
 
 	TRACE_LEAVE(QUIC_EV_CONN_PRSAFRM, qc);
@@ -1502,9 +1508,15 @@
 	 * the current one.
 	 */
 	list_for_each_entry_safe(f, tmp, &origin->reflist, ref) {
-		pn = f->pkt->pn_node.key;
-		TRACE_DEVEL("mark frame as acked from packet",
-		            QUIC_EV_CONN_PRSAFRM, qc, f, &pn);
+		if (f->pkt) {
+			pn = f->pkt->pn_node.key;
+			TRACE_DEVEL("mark frame as acked from packet",
+			            QUIC_EV_CONN_PRSAFRM, qc, f, &pn);
+		}
+		else {
+			TRACE_DEVEL("mark unsend frame as acked",
+			            QUIC_EV_CONN_PRSAFRM, qc, f);
+		}
 		f->flags |= QUIC_FL_TX_FRAME_ACKED;
 		f->origin = NULL;
 		LIST_DELETE(&f->ref);