AP_InertialSensor: fixed default MPU9250 orientation for NavIO

libraries/AP_InertialSensor/AP_InertialSensor_MPU9250.cpp

@@ -283,6 +283,11 @@ bool AP_InertialSensor_MPU9250::update( void )
     // PXF has an additional YAW 180
     accel.rotate(ROTATION_YAW_180);
     gyro.rotate(ROTATION_YAW_180);
+#elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_NAVIO
+    // NavIO has different orientation, assuming RaspberryPi is right
+    // way up, and PWM pins on NavIO are at the back of the aircraft
+    accel.rotate(ROTATION_ROLL_180_YAW_90);
+    gyro.rotate(ROTATION_ROLL_180_YAW_90);
 #endif
 
     _rotate_and_offset_gyro(_gyro_instance, gyro);