virtio_net: Support RX hash XDP hint

The RSS hash report is a feature that's part of the virtio specification.
Currently, virtio backends like qemu, vdpa (mlx5), and potentially vhost
(still a work in progress as per [1]) support this feature. While the
capability to obtain the RSS hash has been enabled in the normal path,
it's currently missing in the XDP path. Therefore, we are introducing
XDP hints through kfuncs to allow XDP programs to access the RSS hash.

1.
https://lore.kernel.org/all/20231015141644.260646-1-akihiko.odaki@daynix.com/#r



Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Reviewed-by: Heng Qi <hengqi@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20240417071822.27831-1-liangchen.linux@gmail.com


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