MAVLink: Remove excessive stack

src/modules/mavlink/mavlink_main.cpp

@@ -2238,7 +2238,7 @@ Mavlink::start(int argc, char *argv[])
 	px4_task_spawn_cmd(buf,
 			   SCHED_DEFAULT,
 			   SCHED_PRIORITY_DEFAULT,
-			   2900,
+			   2800,
 			   (px4_main_t)&Mavlink::start_helper,
 			   (char *const *)argv);