net/mlx5e: RX, Prefetch the xdp_frame data area

A loaded XDP program might write to the xdp_frame data area,
prefetchw() it to avoid a potential cache miss.

Performance tests:
ConnectX-5, XDP_TX packet rate, single ring.
CPU: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz

Before: 13,172,976 pps
After:  13,456,248 pps
2% gain.

Fixes: 22f45398 ("net/mlx5e: Support XDP over Striding RQ")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>