LU-5725 ofd: Expose OFD site_stats through proc

LU-5725 ofd: Expose OFD site_stats through proc

While exposed for the MDT the lu_object cache site stats are not
available for the OFD.  This small patch makes those same stats
available under /proc/fs/lustre/obdfilter/lustre-OST0001/site_stats.

Change-Id: Ic5207d5471cd0f8eacc5a3363c12975c8880224d
Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-on: http://review.whamcloud.com/19247
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>