f2fs: Constrain the modification range of dir_level in the sysfs

The {struct f2fs_sb_info}->dir_level can be modified through the sysfs
interface, but its value range is not limited. If the value exceeds
MAX_DIR_HASH_DEPTH and the mount options include "noinline_dentry",
the following error will occur:
[root@fedora ~]# mount -o noinline_dentry /dev/sdb  /mnt/sdb/
[root@fedora ~]# echo 128 > /sys/fs/f2fs/sdb/dir_level
[root@fedora ~]# cd /mnt/sdb/
[root@fedora sdb]# mkdir test
[root@fedora sdb]# cd test/
[root@fedora test]# mkdir test
mkdir: cannot create directory 'test': Argument list too long

Signed-off-by: Yongpeng Yang <yangyongpeng1@oppo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>