HAL_PX4: implement force_safety_on

libraries/AP_HAL_PX4/RCOutput.cpp

@@ -174,6 +174,12 @@ void PX4RCOutput::set_failsafe_pwm(uint32_t chmask, uint16_t period_us)
     }
 }
 
+bool PX4RCOutput::force_safety_on(void)
+{
+    int ret = ioctl(_pwm_fd, PWM_SERVO_SET_FORCE_SAFETY_ON, 0);
+    return (ret == OK);
+}
+
 void PX4RCOutput::force_safety_off(void)
 {
     int ret = ioctl(_pwm_fd, PWM_SERVO_SET_FORCE_SAFETY_OFF, 0);

libraries/AP_HAL_PX4/RCOutput.h

@@ -21,6 +21,7 @@ public:
     void     read(uint16_t* period_us, uint8_t len);
     void     set_safety_pwm(uint32_t chmask, uint16_t period_us);
     void     set_failsafe_pwm(uint32_t chmask, uint16_t period_us);
+    bool     force_safety_on(void);
     void     force_safety_off(void);
 
     void _timer_tick(void);