Constify

found by flexelint

src/node.c

@@ -291,7 +291,7 @@ tree_free(struct vdp_ctx *vdx, struct node *node)
  */
 
 void
-node_insert(struct bytes_tree *tree, struct node *parent,
+node_insert(const struct bytes_tree *tree, struct node *parent,
     struct node *node)
 {
 	CHECK_OBJ_NOTNULL(tree, BYTES_TREE_MAGIC);

src/node.h

@@ -242,7 +242,7 @@ void node_fill_nodestock(struct ws *, struct node_head *);
 
 struct pesi;
 struct node *node_alloc(struct pesi *);
-void node_insert(struct bytes_tree *, struct node *, struct node *);
+void node_insert(const struct bytes_tree *, struct node *, struct node *);
 void set_closed(struct bytes_tree *, struct node *);
 
 //--------------