net: atlantic: checksum compat issue

Yet another checksum offload compatibility issue was found.

The known issue is that AQC HW marks tcp packets with 0xFFFF checksum
as invalid (1). This is workarounded in driver, passing all the suspicious
packets up to the stack for further csum validation.

Another HW problem (2) is that it hides invalid csum of LRO aggregated
packets inside of the individual descriptors. That was workarounded
by forced scan of all LRO descriptors for checksum errors.

However the scan logic was joint for both LRO and multi-descriptor
packets (jumbos). And this causes the issue.

We have to drop LRO packets with the detected bad checksum
because of (2), but we have to pass jumbo packets to stack because of (1).

When using windows tcp partner with jumbo frames but with LSO disabled
driver discards such frames as bad checksummed. But only LRO frames
should be dropped, not jumbos.

On such a configurations tcp stream have a chance of drops and stucks.

(1) 76f254d4 ("net: aquantia: tcp checksum 0xffff being handled incorrectly")
(2) d08b9a0a ("net: aquantia: do not pass lro session with invalid tcp checksum")

Fixes: d08b9a0a ("net: aquantia: do not pass lro session with invalid tcp checksum")
Signed-off-by: Dmitry Bezrukov <dbezrukov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Dmitry Bogdanov <dbogdanov@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>