ice: Add E830 checksum offload support

E830 supports raw receive and generic transmit checksum offloads.

Raw receive checksum support is provided by hardware calculating the
checksum over the whole packet, regardless of type. The calculated
checksum is provided to driver in the Rx flex descriptor. Then the driver
assigns the checksum to skb->csum and sets skb->ip_summed to
CHECKSUM_COMPLETE.

Generic transmit checksum support is provided by hardware calculating the
checksum given two offsets: the start offset to begin checksum calculation,
and the offset to insert the calculated checksum in the packet. Support is
advertised to the stack using NETIF_F_HW_CSUM feature.

E830 has the following limitations when both generic transmit checksum
offload and TCP Segmentation Offload (TSO) are enabled:

1. Inner packet header modification is not supported. This restriction
   includes the inability to alter TCP flags, such as the push flag. As a
   result, this limitation can impact the receiver's ability to coalesce
   packets, potentially degrading network throughput.
2. The Maximum Segment Size (MSS) is limited to 1023 bytes, which prevents
   support of Maximum Transmission Unit (MTU) greater than 1063 bytes.

Therefore NETIF_F_HW_CSUM and NETIF_F_ALL_TSO features are mutually
exclusive. NETIF_F_HW_CSUM hardware feature support is indicated but is not
enabled by default. Instead, IP checksums and NETIF_F_ALL_TSO are the
defaults. Enforcement of mutual exclusivity of NETIF_F_HW_CSUM and
NETIF_F_ALL_TSO is done in ice_set_features(). Mutual exclusivity
of IP checksums and NETIF_F_HW_CSUM is handled by netdev_fix_features().

When NETIF_F_HW_CSUM is requested the provided skb->csum_start and
skb->csum_offset are passed to hardware in the Tx context descriptor
generic checksum (GCS) parameters. Hardware calculates the 1's complement
from skb->csum_start to the end of the packet, and inserts the result in
the packet at skb->csum_offset.

Co-developed-by: Alice Michael <alice.michael@intel.com>
Signed-off-by: Alice Michael <alice.michael@intel.com>
Co-developed-by: Eric Joyner <eric.joyner@intel.com>
Signed-off-by: Eric Joyner <eric.joyner@intel.com>
Signed-off-by: Paul Greenwalt <paul.greenwalt@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Rinitha S <sx.rinitha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20250310174502.3708121-2-anthony.l.nguyen@intel.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>