NAME
        IND_SETMPORT -- Set the current mouse port

   FUNCTION
        This command sets the gameport port at which the mouse is
        connected.

   IO REQUEST
        io_Message      mn_ReplyPort set if quick I/O is not possible
        io_Device       preset by the call to opendevice
        io_Unit         preset by the call to opendevice
        io_Command      IND_SETMPORT
        io_Flags        IOB_QUICK set if quick I/O is possible
        io_Length       1
        io_Data         a pointer to a byte that is either 0 or 1,
                        indicating that mouse input should be obtained
                        from either the left or right controller port,
                        respectively.