mlx4_en: Adjusting moderation per each ring

Moderation is now done per ring and coalescing is enabled
by set_ring_param in ethtool.

Signed-off-by: Alexander Guller <alexg@mellanox.co.il>
Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>