Fix infiniband QDR or FDR troubles on fat memory machines.

Fix memory trouble on FAT machines:
The formula to computer the maximum value of pagepool when using RDMA is:   
2^log_num_mtt  x  2^log_mtts_per_seg * x PAGE_SIZE > ( 2x pagepool )

2^20 bytes x 2^4 x 4K = 64GiB
Add:
/etc/modprobe.d/mlx4_core.conf
options mlx4_core log_num_mtt=20 log_mtts_per_seg=4
check changes

more /sys/module/mlx4_core/parameters/log_num_mtt

more /sys/module/mlx4_core/parameters/log_mtts_per_seg