net: lwip: tftp: add support of tsize option to client

net: lwip: tftp: add support of tsize option to client

The TFTP server can report the size of the entire file that is about to
be received in the Transfer Size Option, this is described in RFC 2349.
This functionality is optional and the server may not report tsize in
case it is not supported.

Always send tsize request to the server to query the transfer size,
and in case the server does respond, cache that information locally
in tftp_state.tsize, otherwise cache size 0. Introduce new function
tftp_client_get_tsize() which returns the cached tftp_state.tsize so
clients can determine the transfer size and use it.

Update net/lwip/tftp.c to make use of tftp_client_get_tsize() and
avoid excessive printing of '#' during TFTP transfers in case the
transfer size is reported by the server.

Submitted upstream: https://savannah.nongnu.org/patch/index.php?item_id=10557

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Acked-by: Jerome Forissier <jerome.forissier@arm.com>