The u-boot TFTP client will fail a fully completed file retrieval if the
final ACK gets an ICMP response that the port is unavailable which can
occur if the port is closed before the ACK arrives from the client. This
change causes the TFTP server to wait for the final ACK before closing
the socket and prevents transfers from failing due to the race
condition.
- Add a --show-backtrace option to make it easier for users to
get an exception backtrace if something goes wrong.
- Fix the --packet-trace option so it actually decodes the packets
