f2fs: fix to use inline space only if inline_xattr is enable

f2fs: fix to use inline space only if inline_xattr is enable

With below mkfs and mount option:

MKFS_OPTIONS  -- -O extra_attr -O project_quota -O inode_checksum -O flexible_inline_xattr -O inode_crtime -f
MOUNT_OPTIONS -- -o noinline_xattr

We may miss xattr data with below testcase:
- mkdir dir
- setfattr -n "user.name" -v 0 dir
- for ((i = 0; i < 190; i++)) do touch dir/$i; done
- umount
- mount
- getfattr -n "user.name" dir

user.name: No such attribute

The root cause is that we persist xattr data into reserved inline xattr
space, even if inline_xattr is not enable in inline directory inode, after
inline dentry conversion, reserved space no longer exists, so that xattr
data missed.

Let's use inline xattr space only if inline_xattr flag is set on inode
to fix this iusse.

Fixes: 6afc662e68b5 ("f2fs: support flexible inline xattr size")
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>