LU-822 osd: use bitmask to calculate seq hash

LU-822 osd: use bitmask to calculate seq hash

We are using mod to hash seq to different OI files, which is not
allowed on 32-bit arch because seq is 64-bit. It can be resolved
by limit oi_count to power2 and use bitmask to calculate seq hash.
This patch also renamed modparameter osd_oi_num to osd_oi_count.

Signed-off-by: Liang Zhen <liang@whamcloud.com>
Change-Id: I61c1fac65a33c78b5b5196d2b2d6fd5519deffda
Reviewed-on: http://review.whamcloud.com/1941
Tested-by: Hudson
Reviewed-by: Mikhail Pershin <tappro@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>