navigator: increase stack

The stack size was generally ok but seemed to get exhausted in the case
of a waypoint which is too far away and therefore exercises some more
code in the mission feasability checker.

Generally, we should have more margin in the navigator stack size
because there are a bunch of different code paths that can happen.

src/modules/navigator/navigator_main.cpp

@@ -673,7 +673,7 @@ Navigator::start()
 	_navigator_task = px4_task_spawn_cmd("navigator",
 					 SCHED_DEFAULT,
 					 SCHED_PRIORITY_DEFAULT + 5,
-					 1300,
+					 1600,
 					 (px4_main_t)&Navigator::task_main_trampoline,
 					 nullptr);