net/mlx5: Correctly set gso_segs when LRO is used

When gso_segs is left at 0, a number of assumptions will end up being
incorrect throughout the stack.

For example, in the GRO-path, we set NAPI_GRO_CB()->count to gso_segs.
So, if a non-LRO'ed packet followed by an LRO'ed packet is being
processed in GRO, the first one will have NAPI_GRO_CB()->count set to 1 and
the next one to 0 (in dev_gro_receive()).
Since commit 531d0d32
("net/mlx5: Correctly set gso_size when LRO is used")
these packets will get merged (as their gso_size now matches).
So, we end up in gro_complete() with NAPI_GRO_CB()->count == 1 and thus
don't call inet_gro_complete(). Meaning, checksum-validation in
tcp_checksum_complete() will fail with a "hw csum failure".

Even before the above mentioned commit, incorrect gso_segs means that other
things like TCP's accounting of incoming packets (tp->segs_in,
data_segs_in, rcv_ooopack) will be incorrect. Which means that if one
does bytes_received/data_segs_in, the result will be bigger than the
MTU.

Fix this by initializing gso_segs correctly when LRO is used.

Fixes: e586b3b0 ("net/mlx5: Ethernet Datapath files")
Reported-by: Gal Pressman <gal@nvidia.com>
Closes: https://lore.kernel.org/netdev/6583783f-f0fb-4fb1-a415-feec8155bc69@nvidia.com/


Signed-off-by: Christoph Paasch <cpaasch@openai.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250729-mlx5_gso_segs-v1-1-b48c480c1c12@openai.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>