LU-506 FC15: update shrinker to use shrink_control callback

LU-506 FC15: update shrinker to use shrink_control callback

Linux 3.0 memory pressure shrinker now takes "struct shrink_control" as
its argument instead of "nr_to_scan" and "gfp_mask". This was backported
to Fedora 15.

Signed-off-by: Yang Sheng <ys@whamcloud.com>
Change-Id: Id9f6a9e10efe785d2837d1ad73098d2808a2f076
Reviewed-on: http://review.whamcloud.com/1331
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>