Chain Send Command (Net Bios, 17h)

        The CHAIN SEND command is similar to the SEND command, except the
        data to be transferred is contained in two separate buffers.
        CHAIN send concatenates these buffers -- the receiving end will
        see one message. The first part of the message is defined by
        BUFADR and BUFLEN. The address of the second part is stored in a
        double word at CALLNAME+2. The length of the second part is
        stored in a word at CALLNAME+0. The total length cannot exceed
        65535 bytes.