INT 2F U - NETWORK REDIRECTOR - PRINTER ON/OFF???
        AX = 1126h
        ES:DI -> SFT for file handle 4???
        SS = DOS DS???
        ???
Return: CF set on error
Notes:  called by DOS 3.1+ kernel
        called when print echoing (P, PrtSc) changes state and STDPRN has
          bit 11 of the device information word in the SFT set