AP_CANManager: chane KDECAN enum from 2 to 8

This is to force users to realise that something has changed in the hopes they will read the 4.1 release notes

libraries/AP_CANManager/AP_CANDriver.cpp

@@ -32,7 +32,7 @@ const AP_Param::GroupInfo AP_CANManager::CANDriver_Params::var_info[] = {
     // @Param: PROTOCOL
     // @DisplayName: Enable use of specific protocol over virtual driver
     // @Description: Enabling this option starts selected protocol that will use this virtual driver
-    // @Values{Copter,Plane,Sub}: 0:Disabled,1:UAVCAN,2:KDECAN,3:ToshibaCAN,4:PiccoloCAN,5:CANTester
+    // @Values{Copter,Plane,Sub,Rover}: 0:Disabled,1:UAVCAN,3:ToshibaCAN,4:PiccoloCAN,5:CANTester,8:KDECAN
     // @Values: 0:Disabled,1:UAVCAN,3:ToshibaCAN,4:PiccoloCAN,5:CANTester,6:EFI_NWPMU,7:USD1
     // @User: Advanced
     // @RebootRequired: True

libraries/AP_CANManager/AP_CANManager.h

@@ -53,12 +53,13 @@ public:
     enum Driver_Type : uint8_t {
         Driver_Type_None = 0,
         Driver_Type_UAVCAN = 1,
-        Driver_Type_KDECAN = 2,
+        // 2 was KDECAN -- do not re-use
         Driver_Type_ToshibaCAN = 3,
         Driver_Type_PiccoloCAN = 4,
         Driver_Type_CANTester = 5,
         Driver_Type_EFI_NWPMU = 6,
         Driver_Type_USD1 = 7,
+        Driver_Type_KDECAN = 8,
     };
 
     void init(void);