LU-1994 kernel: 3.6 dentry_open uses struct path as first arg

3.6 dentry_open uses struct path as first argument.
see kernel commit 765927b2 for details.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Change-Id: Ib69021356b1483abfcc49f644260b1dcbb57f76b
Reviewed-on: http://review.whamcloud.com/4386
Tested-by: Hudson
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>