[syslinux] Allwell doesn't respond to OACK with ACK in TFTP

[Neologism]

I'm trying to network-boot a GCT Allwell set-top box without success. 
My frustration level is high.

The problem seems to be that the Allwell is sending a RRQ with an
option.  tftp-hpa responds with an OACK, and waits for the corresponding
ACK from the Allwell.  The Allwell never sends that ACK, but instead
continues with the same RRQ until timeout.

Having read RFC1782, this makes me think the TFTP client in the Allwell
is broken.  Ack! Ack ack ack ack ack.  Ack, thpppht.  What do I do?

The packets follow:

RRQ:

    Trivial File Transfer Protocol
        Opcode: Read Request (1)
        Source File: pxelinux.0
        Type: octet
        Option: blksize = 1456
    
OACK:

    Trivial File Transfer Protocol
        Opcode: Option Acknowledgement (6)
        Option: blksize = 1456