INT 21 - TopWare Network OS v5.10+ - GET SHARING STATUS OF PRINTER SERVER
        AX = FFC3h
Return: AL = sharing status of printers (see below)
            FFh if not a printer server

Bitfields for printer sharing status:
 bit 0  LPT1 is shared
 bit 1  LPT2 is shared
 bit 2  LPT3 is shared

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