net/mlx4_core: the number of MTTs should consider log_mtts_per_seg

net/mlx4_core: the number of MTTs should consider log_mtts_per_seg

No matter how we decided how many MTTs will be used (calculation
from system memory or using default value), we need to consider
the number of MTTs per segment.

This will allow the user to specify how many MTTs will be used
(with log_num_mtt) and how many MTTs will be used per segment
(using log_mtts_per_seg).

Signed-off-by: Dotan Barak <dotanb@dev.mellanox.co.il>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
(Ported from Mellanox OFED 2.4)

Signed-off-by: Mukesh Kacker <mukesh.kacker@oracle.com>