virtio-net: ethtool configurable RXCSUM

virtio-net: ethtool configurable RXCSUM

Allow user configuring RXCSUM separately with ethtool -K,
reusing the existing virtnet_set_guest_offloads helper
that configures RXCSUM for XDP. This is conditional on
VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.

If Rx checksum is disabled, LRO should also be disabled.

Signed-off-by: Tonghao Zhang <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Acked-by: Jason Wang <[email protected]>
Acked-by: Willem de Bruijn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>