AP_HAL_PX4: moved size of main thread stack to Scheduler.h

make it more obvious

libraries/AP_HAL_PX4/HAL_PX4_Class.cpp

@@ -234,7 +234,7 @@ void HAL_PX4::init(int argc, char * const argv[]) const
             daemon_task = task_spawn_cmd(SKETCHNAME,
                                          SCHED_FIFO,
                                          APM_MAIN_PRIORITY,
-                                     8192,
+                                         APM_MAIN_THREAD_STACK_SIZE,
                                          main_loop,
                                          NULL);
             exit(0);

libraries/AP_HAL_PX4/Scheduler.h

@@ -19,6 +19,8 @@
 #define APM_OVERTIME_PRIORITY 10
 #define APM_STARTUP_PRIORITY  10
 
+#define APM_MAIN_THREAD_STACK_SIZE 8192
+
 /* Scheduler implementation: */
 class PX4::PX4Scheduler : public AP_HAL::Scheduler {
 public: