LU-9129 llite: ignore layout for ll_writepages()

LU-9129 llite: ignore layout for ll_writepages()

ll_writepages() would be called inside the direct IO context and
if the layout has been changed during this time, the layout_conf()
has to wait for active IO to complete before applying the layout
change, this is a case of deadlock.

It should ignore layout to avoid this problem. This is safe as long
as pages exist, the layout won't be changed on this client.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I457133a4a30215b8513d5eaec449fc129cc43a3e
Reviewed-on: https://review.whamcloud.com/25474
Tested-by: Jenkins
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>