net/mlx5e: XDP, Consider large muti-buffer packets in Striding RQ params calculations

Function mlx5e_rx_get_linear_stride_sz() returns PAGE_SIZE immediately
in case an XDP program is attached. The more accurate formula is
ALIGN(sz, PAGE_SIZE), to prevent two packets from residing on the same
page.

The assumption behind the current code is that sz <= PAGE_SIZE holds for
all cases with XDP program set.

This is true because it is being called from:
- 3 times from Striding RQ flows, in which XDP is not supported for such
  large packets.
- 1 time from Legacy RQ flow, under the condition
  mlx5e_rx_is_linear_skb().

No functional change here, just removing the implied assumption in
preparation for supporting XDP multi-buffer in Striding RQ.

Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>