LU-2484 obd: add md_stats to MDC and LMV devices

LU-2484 obd: add md_stats to MDC and LMV devices

Enable md_stats for MDC and LMV devices and fix the definition of
EXP_MD_COUNTER_INCREMENT() so that they will be tallied. These stats
track usage of the md_ops methods (from the OBD layer, not to be
confused with md_device methods) and are exported through the files
/proc/fs/lustre/{lmv,mdc}/*/md_stats.

Rename m_sync to m_fsync making the counter name (fsync) more
intuitive. Prune the minimally useful operations from set of md_ops to
be counted. The operations counted are close, create, enqueue,
getattr, intent_lock, link, rename, setattr, fsync, readpage, unlink,
setxattr, egtxattr, intent_getattr_async, and revalidate_lock.

Add assertions to lprocfs_counter_{add,sub}() to ensure that the
counter index lies in the appropriate range for stats. Remove the
corresponding assertions from OBD_COUNTER_INCREMENT(),
EXP_COUNTER_INCREMENT(), and EXP_MD_COUNTER_INCREMENT(). Add macros
NUM_OBD_STATS and NUM_MD_STATS for use when allocating stats.

In mdt_export_stats_init() allocate and initialize the nid_stats
member of struct exp_nid_stats using only the MDT private
counters. This does not affect the contents of
/proc/fs/lustre/mdt/*/exports/*/stats but does save memory.

Add a flag to struct obd_device to indicate if EXP_COUNTER_INCREMENT()
should increment stats in the nid_stats member (as in the case of OFD)
or not (MDT).

Remove the unused member exp_md_stats from struct obd_export.

Signed-off-by: John L. Hammond <jhammond@tacc.utexas.edu>
Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Idccd30e13adbc11d10b544cdfbe1d23123176e94
Reviewed-on: http://review.whamcloud.com/4827
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>