add MSG_SET_LINEAR_COUNT back again at 0x19

Firmware/communication/can/can_simple.cpp

@@ -141,6 +141,9 @@ void CANSimple::do_command(Axis& axis, const can_Message_t& msg) {
         case MSG_CLEAR_ERRORS:
             clear_errors_callback(axis, msg);
             break;
+        case MSG_SET_LINEAR_COUNT:
+            set_linear_count_callback(axis, msg);
+            break;
         default:
             break;
     }

Firmware/communication/can/can_simple.hpp

@@ -32,6 +32,7 @@ class CANSimple {
         MSG_RESET_ODRIVE,
         MSG_GET_VBUS_VOLTAGE,
         MSG_CLEAR_ERRORS,
+        MSG_SET_LINEAR_COUNT,
         MSG_CO_HEARTBEAT_CMD = 0x700,  // CANOpen NMT Heartbeat  SEND
     };