control: keep track of prop_id

Keep track of the property id which describes the property
functionality.
Link controls based on the property instead of the param_id.

src/pipewire/private.h

@@ -424,6 +424,7 @@ struct pw_control {
 	struct spa_list inputs_link;	/**< link in linked input control */
 
 	uint32_t id;
+	uint32_t prop_id;
 	int32_t size;
 
 	struct spa_hook_list listener_list;