cdc_ncm: Fix tx_bytes statistics
cdc_ncm: Fix tx_bytes statistics

The tx_curr_frame_payload field is u32. When we try to calculate a
small negative delta based on it, we end up with a positive integer
close to 2^32 instead.  So the tx_bytes pointer increases by about
2^32 for every transmitted frame.

Fix by calculating the delta as a signed long.

Cc: Ben Hutchings <a9aff6bdb06df0f1e86a184e2c263c6782eaee6c@codethink.co.uk>
Reported-by: Florian Bruhin <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@the-compiler.org>
Fixes: 7a1e890e2168 ("usbnet: Fix tx_bytes statistic running backward in cdc_ncm")
Signed-off-by: Bjørn Mork <8a2957e0063f2abf61bd145b6236a74a3708ac54@mork.no>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs