net/mlx5e: xsk: Use XSK frame size as striding RQ page size

XSK RQs support striding RQ linear mode, but the stride size is always
set to PAGE_SIZE. It may be larger than the XSK frame size,
unnecessarily reducing the useful space in a WQE, but more importantly
causing UMEM data corruption in certain cases.

Normally, stride size bigger than XSK frame size is not a problem if the
hardware enforces the MTU. However, traffic between vports skips the
hardware MTU check, and oversized packets may be received.

If an oversized packet is bigger than the XSK frame but not bigger than
the stride, it will cause overwriting of the adjacent UMEM region. If
the packet takes more than one stride, they can be recycled for reuse
so it's not a problem when the XSK frame size matches the stride size.

To reduce the impact of the above issue, attempt to use the MTT page
size for striding RQ that matches the XSK frame size, allowing to safely
use 2048-byte frames on an up-to-date firmware.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>