LU-2479 ldiskfs: do not check dir max size for regular files

LU-2479 ldiskfs: do not check dir max size for regular files

ldiskfs_append() is used not only to extend directory but also to
maintain iam container. In later case ldiskfs_append() should not
check for max directory size. The iam container is distunguished as
regular file.

Signed-off-by: Vladimir Saveliev <vladimir_saveliev@xyratex.com>
Change-Id: I205b0b1149d7bd477b3965ce68a546dfd9dc6a6f
Reviewed-on: http://review.whamcloud.com/8137
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alexey Lyashkov <alexey_lyashkov@xyratex.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>