LU-9841 lov: do not split IO for single striped file

LU-9841 lov: do not split IO for single striped file

stripe size for single striped file is not reliable, it shouldn't
be used to split I/O.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I47c31d59b46b07d4a6760b8985e1c19da4765a5c
Reviewed-on: https://review.whamcloud.com/28451
Tested-by: Jenkins
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>