net/mlx5: remove excessive data prefetch

net/mlx5: remove excessive data prefetch

In Enhanced Multi-Packet Send (eMPW), entire packet data is prefetched to
LLC if it isn't inlined. Even though this helps reducing jitter when HW
fetches data by DMA, this can thresh the LLC with evicting precious data.
And if the size of queue is large and there are many queues, this might not
be effective. Also, if application runs on a remote node from the PCIe
link, it may not be helpful and can even cause bad results.

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>