FTP driver - access type

        Entry:
          AH = 02h
          AL = interface class
          BX = interface type
          DL = interface number
          DS:SI -> type
          CX = length of type
          ES:DI -> receiver
        Return:
          CF set on error
            DH = error code (see AX=01FFh)
          CF clear if successful
            AX = handle

        Receiver is called with

          AX = subfunction
              00h application to return pointer to buffer in ES:DI
                  ES:DI = 0000h:0000h means throw away packet
              01h copy to DS:SI buffer completed
          BX = handle
          CX = buffer length

        when a packet is received