xfs: devirtualize ->sf_entsize and ->sf_nextentry

mainline inclusion
from mainline-5.5-rc1
commit 50f6bb6b
category: bugfix
bugzilla: 31596
CVE: NA

---------------------------

Just check for file-type enabled directories directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Conflicts:
	fs/xfs/libxfs/xfs_dir2_priv.h
	fs/xfs/libxfs/xfs_dir2_sf.c
	fs/xfs/xfs_dir2_readdir.c
[zb: since patch 84915e1b, 707e0dda, e91ec882, 04df34ac
 not merged, adjust code]

Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>