AP_InertialSensor_MPU6000: Fix the test code so that compiles.

libraries/AP_InertialSensor/examples/MPU6000/MPU6000.pde

@@ -28,6 +28,8 @@
 #include <AP_ADC_AnalogSource.h>
 #include <AP_Compass.h>
 #include <AP_Declination.h>
+#include <AP_NavEKF.h>
+#include <AP_HAL_Linux.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;
 AP_InertialSensor_MPU6000 ins;