Receive Datagram Command (Net Bios, 21h)

        This command waits for a SEND DATAGRAM to the name associated
        with the NUM field (may be a group name). An 0FFh in the NUM
        field is used to receive all datagrams to the machine. The
        BUFADR and BUFLEN fields are set to the size and maximum length
        of the receive data buffer. There is no time-out on this
        command. The name of the sender is returned in CALLNAME.

        The actual size of the received data is returned in BUFLEN. If
        the maximum buffer length was smaller than the length of the
        data, then the buffer is filled to the maximum and RETCODE = 06h
        is returned. The remaining data is lost.