net/mlx5e: kTLS, Use CHECKSUM_UNNECESSARY for device-offloaded packets

For RX TLS device-offloaded packets, the HW spec guarantees checksum
validation for the offloaded packets, but does not define whether the
CQE.checksum field matches the original packet (ciphertext) or
the decrypted one (plaintext). This latitude allows architetctural
improvements between generations of chips, resulting in different decisions
regarding the value type of CQE.checksum.

Hence, for these packets, the device driver should not make use of this CQE
field. Here we block CHECKSUM_COMPLETE usage for RX TLS device-offloaded
packets, and use CHECKSUM_UNNECESSARY instead.

Value of the packet's tcp_hdr.csum is not modified by the HW, and it always
matches the original ciphertext.

Fixes: 1182f365

 ("net/mlx5e: kTLS, Add kTLS RX HW offload support")
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>