mlx4: dma_dir is a mlx4_en_priv attribute

No need to duplicate it for all queues and frags.

num_frags & log_rx_info become u8 to save space.
u8 accesses are a bit faster than u16 anyway.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>