AP_HAL: rename AP_HAL::CAN to AP_HAL::CANHal

avoid conflict with ChibiOS STM32F3xx headers

libraries/AP_HAL/AP_HAL_Namespace.h

@@ -31,7 +31,7 @@ namespace AP_HAL {
 
     class CANProtocol;
     class CANManager;
-    class CAN;
+    class CANHal;
 
     class Util;
     class Flash;

libraries/AP_HAL/CAN.h

@@ -48,7 +48,7 @@ public:
 /**
  * Single non-blocking CAN interface.
  */
-class AP_HAL::CAN: public uavcan::ICanIface {
+class AP_HAL::CANHal: public uavcan::ICanIface {
 public:
     /*  CAN port open method