MINOR: trace: add quic_conn argument definition

Prepare trace support for quic_conn instances as argument. This will be
used by the xprt-quic layer in replacement of the connection.

This commit is part of the rearchitecture of xprt-quic layers and the
separation between xprt and connection instances.
diff --git a/src/trace.c b/src/trace.c
index f075787..15e0148 100644
--- a/src/trace.c
+++ b/src/trace.c
@@ -86,6 +86,9 @@
 	const struct stream *strm = NULL;
 	const struct connection *conn = NULL;
 	const struct check *check = NULL;
+#ifdef USE_QUIC
+	const struct quic_conn *qc = NULL;
+#endif
 	const void *lockon_ptr = NULL;
 	struct ist ist_func = ist(func);
 	char tnum[4];
@@ -112,6 +115,11 @@
 	if (src->arg_def & TRC_ARGS_CHK)
 		check = trace_pick_arg(src->arg_def & TRC_ARGS_CHK, a1, a2, a3, a4);
 
+#ifdef USE_QUIC
+	if (src->arg_def & TRC_ARGS_QCON)
+		qc = trace_pick_arg(src->arg_def & TRC_ARGS_QCON, a1, a2, a3, a4);
+#endif
+
 	if (!sess && strm)
 		sess = strm->sess;
 	else if (!sess && conn)
@@ -171,6 +179,9 @@
 		case TRACE_LOCKON_STREAM:     lockon_ptr = strm; break;
 		case TRACE_LOCKON_CHECK:      lockon_ptr = check; break;
 		case TRACE_LOCKON_THREAD:     lockon_ptr = ti;   break;
+#ifdef USE_QUIC
+		case TRACE_LOCKON_QCON:       lockon_ptr = qc;   break;
+#endif
 		case TRACE_LOCKON_ARG1:       lockon_ptr = a1;   break;
 		case TRACE_LOCKON_ARG2:       lockon_ptr = a2;   break;
 		case TRACE_LOCKON_ARG3:       lockon_ptr = a3;   break;