LU-1319 mdt: increment MDT getattr stats

LU-1319 mdt: increment MDT getattr stats

Move increment of MDT getattr stat from mdt_getattr() to
mdt_getattr_internal() so we don't miss other call paths
that may service getattr requests.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: yang sheng <ys@whamcloud.com>
Change-Id: I25293fe98567b1250ecc2f9645295c1522345295
Reviewed-on: http://review.whamcloud.com/2637
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>