Navigator: Fix priority to run at much lower priority than controllers, but...

Navigator: Fix priority to run at much lower priority than controllers, but higher than common stuff.

src/modules/navigator/navigator_main.cpp

@@ -524,7 +524,7 @@ Navigator::start()
 	/* start the task */
 	_navigator_task = px4_task_spawn_cmd("navigator",
 					 SCHED_DEFAULT,
-					 SCHED_PRIORITY_DEFAULT - 5,
+					 SCHED_PRIORITY_DEFAULT + 5,
 					 1500,
 					 (px4_main_t)&Navigator::task_main_trampoline,
 					 nullptr);