INT 21 P - Phar Lap 386/DOS-Extender - RESET DOS EXTENDER DATA STRUCTURES
        AX = 2501h
        SS = application's original SS or DS (FlashTek X-32VM)
Return: CF clear if successful
        CF set on error
            caller is operating on X-32 stack (FlashTek X-32VM)
Notes:  Phar Lap uses INT 21/AH=25h as the entry point for all 386/DOS-Extender
          system calls.  Only available when directly using 386/DOS-Extender or
          a compatible DOS extender, or when using a product that was created
          using 386-DOS/Extender or a compatible
        this function is also supported by FlashTek X-32VM