#112 faill with gcc15

[Petr Gajdos]

Following fixes the build for me:

--- etherape-0.9.20.orig/src/diagram.c  2025-07-08 13:55:41.686008017 +0000
+++ etherape-0.9.20/src/diagram.c   2025-07-08 13:56:34.093020024 +0000
@@ -170,7 +170,7 @@ static void update_diagram(GooCanvas *ca
 static void diagram_update_nodes(GooCanvas *canvas); /* updates ALL nodes */
 static void diagram_update_links(GooCanvas *canvas); /* updates ALL links */
 static void diagram_update_background_image(GooCanvas *canvas); /* updates background image */
-static void diagram_reposition(); /* reposition nodes */
+static void diagram_reposition(GooCanvas *canvas); /* reposition nodes */

 static void check_new_protocol(GtkWidget *prot_table, const protostack_t *pstk);
 static gint check_new_node(node_t *node, GooCanvas *canvas);

[R. Ghetta]

applied, many thanks