f2fs: enable inline_xattr by default

In android, since SElinux is enable, security policy will be appliedd for
each file, it stores in inode as an xattr entry, so it will take one 4k
size node block additionally for each file.

Let's enable inline_xattr by default in order to save storage space.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>