AP_HAL_Linux: rename system_initialized() and add is_system_initialized()

libraries/AP_HAL_Linux/HAL_Linux_Class.cpp

@@ -384,7 +384,7 @@ void HAL_Linux::run(int argc, char* const argv[], Callbacks* callbacks) const
     // NOTE: See commit 9f5b4ffca ("AP_HAL_Linux_Class: Correct
     // deadlock, and infinite loop in setup()") for details about the
     // order of scheduler initialize and setup on Linux.
-    scheduler->system_initialized();
+    scheduler->set_system_initialized();
 
     // possibly load external modules
 #if AP_MODULE_SUPPORTED

libraries/AP_HAL_Linux/Scheduler.cpp

@@ -292,10 +292,10 @@ void Scheduler::_wait_all_threads()
     }
 }
 
-void Scheduler::system_initialized()
+void Scheduler::set_system_initialized()
 {
     if (_initialized) {
-        AP_HAL::panic("PANIC: scheduler::system_initialized called more than once");
+        AP_HAL::panic("PANIC: scheduler::set_system_initialized called more than once");
     }
 
     _initialized = true;

libraries/AP_HAL_Linux/Scheduler.h

@@ -36,7 +36,8 @@ public:
 
     void     register_timer_failsafe(AP_HAL::Proc, uint32_t period_us) override;
 
-    void     system_initialized() override;
+    void     set_system_initialized() override;
+    bool     is_system_initialized() override { return _initialized; };
 
     void     reboot(bool hold_in_bootloader) override;