bnx2x: fix checksum validation

bnx2x: fix checksum validation

bnx2x driver incorrectly sets ip_summed to CHECKSUM_UNNECESSARY on
encapsulated segments. TCP stack happily accepts frames with bad
checksums, if they are inside a GRE or IPIP encapsulation.

Our understanding is that if no IP or L4 csum validation was done by the
hardware, we should leave ip_summed as is (CHECKSUM_NONE), since
hardware doesn't provide CHECKSUM_COMPLETE support in its cqe.

Then, if IP/L4 checksumming was done by the hardware, set
CHECKSUM_UNNECESSARY if no error was flagged.

Patch based on findings and analysis from Robert Evans

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Eilon Greenstein <[email protected]>
Cc: Yaniv Rosner <[email protected]>
Cc: Merav Sicron <[email protected]>
Cc: Tom Herbert <[email protected]>
Cc: Robert Evans <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Acked-by: Eilon Greenstein <[email protected]>
Signed-off-by: David S. Miller <[email protected]>