LU-5014 osd-ldiskfs: vfs_unlink api changed

LU-5014 osd-ldiskfs: vfs_unlink api changed

In newer kernels the vfs_unlink api changed to take
more arguments.  This patch creates a wrapper to let us adapt
to the different versions of vfs_unlink in old and new kernels.
As vfs_unlink is only used in server code
this only impacts server builds of lustre.

Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Change-Id: I3aa9a305530f74ee010fa5173527a37e048a9ef8
Reviewed-on: http://review.whamcloud.com/10235
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>