mlx5_core: Change optimal_reclaimed_pages for better performance

Change optimal_reclaimed_pages() to increase the output size of each
reclaim pages command. This change reduces significantly the amount of
reclaim pages commands issued to FW when the driver is unloaded which
reduces the overall driver unload time.

Signed-off-by: Moshe Lazer <moshel@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>