LU-14043 llite: allow DIO with unaligned IO count

LU-14043 llite: allow DIO with unaligned IO count

DIO only require user buffer page aligned and
IO offset page aligned, it is ok that io count is
not page aligned, remove this unnecessary limit
so that we could use DIO with file not aligned
with PAGE SIZE.

Change-Id: Iaf1e224b3f180f91d1b54016c6e6b7adaf674bf8
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/40392
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>