#1 tftp client, lost acks = timeout

[Brenda J. Butler]

When the tftp client downloads a file, if the ack is
sent by the client but not received by the server, then
the tftp transfer stops. The server re-sends the last
block, but the client expects the next block and
ignores the last block. The server resends several
times, then the transfer ends unsuccessfully.

This patch will treat the repeated block the same as a
normally transferred block (will send the ack) but will
not save the contents to the download-stream. Thus the
ack will be re-sent to the server, and the server will
send the next block, and the transfer will continue.

The problem was observed and diagnosed by John
McCarthy, and the fix was coded by Brenda J. Butler.

[Brenda J. Butler]

patch to uboot to fix tftp client timeouts on lost acks