xfs: rename bulkstat functions

Rename the bulkstat functions to 'fsbulkstat' so that they match the
ioctl names.  We will be introducing a new set of bulkstat/inumbers
ioctls soon, and it will be important to keep the names straight.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>