permissions: check permissions more

Pass client to some core functions to make it possible to check
permissions when iterating globals.
Check permissions of factory before using it.
Check permissions in link factory, only allow linking of nodes we can
see.
Check permissions in the autolink module, only try to link to nodes
we can see.
Make client permissions update behave like an atomic update of an
unordered set of permissions, which is perhaps a bit more intuitive.

spa/include/spa/utils/dict.h

@@ -36,6 +36,8 @@ struct spa_dict_item {
 	const char *value;
 };
 
+#define SPA_DICT_ITEM_INIT(key,value) (struct spa_dict_item) { key, value }
+
 struct spa_dict {
 	const struct spa_dict_item *items;
 	uint32_t n_items;