net/mlx4_core: Allow MTTs starting at any index

Allow obtaining MTTs starting at any index,
thus give a better cache utilization.

For this, allow setting log_mtts_per_seg to 0, and use
this in default.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: Anaty Rahamim Bar Kat <anaty@mellanox.com>
Reviewed-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>