INT 21 - LANtastic v4.1+ - GET/SET SERVER CONTROL BITS
        AX = 5FCCh
        ES:DI -> ASCIZ server name in form "\\machine"
        CX = bit values (value of bits you want to set)  See below.
        DX = bit mask (bits you are interested in, 0 = get only)  See
below.
Return: CF clear if successful
            CX = control bits after call
                bit 0: disable logins
        CF set on error
            AX = error code
Note:   you must have the "S" privilege to SET, anyone can GET.