AP_Volz_Protocol: allow Volz protocol to be compiled out

libraries/AP_Volz_Protocol/AP_Volz_Protocol.cpp

@@ -4,13 +4,14 @@
  *  Created on: Oct 31, 2017
  *      Author: guy
  */
-#include <AP_HAL/AP_HAL.h>
-#include <SRV_Channel/SRV_Channel.h>
-
 #include "AP_Volz_Protocol.h"
-#if NUM_SERVO_CHANNELS
+
+#if AP_VOLZ_ENABLED
+
+#include <AP_HAL/AP_HAL.h>
 
 #include <AP_SerialManager/AP_SerialManager.h>
+#include <SRV_Channel/SRV_Channel.h>
 
 extern const AP_HAL::HAL& hal;
 
@@ -158,4 +159,5 @@ void AP_Volz_Protocol::update_volz_bitmask(uint32_t new_bitmask)
 
     volz_time_frame_micros = channels_micros;
 }
-#endif //NUM_SERVO_CHANNELS
+
+#endif  // AP_VOLZ_ENABLED

libraries/AP_Volz_Protocol/AP_Volz_Protocol.h

@@ -33,6 +33,14 @@
 
 #pragma once
 
+#include <AP_HAL/AP_HAL_Boards.h>
+
+#ifndef AP_VOLZ_ENABLED
+#define AP_VOLZ_ENABLED 1
+#endif
+
+#if AP_VOLZ_ENABLED
+
 #include <AP_HAL/AP_HAL.h>
 #include <AP_Param/AP_Param.h>
 
@@ -73,3 +81,5 @@ private:
     AP_Int32 bitmask;
     bool initialised;
 };
+
+#endif  // AP_VOLZ_PROTOCOL