ceph: include preferred_osd in file layout virtual xattr

static size_t ceph_vxattrcb_layout(struct ceph_inode_info *ci, char *val,

				   size_t size)

{

	return snprintf(val, size,

	int ret;

	ret = snprintf(val, size,

		"chunk_bytes=%lld\nstripe_count=%lld\nobject_size=%lld\n",

		(unsigned long long)ceph_file_layout_su(ci->i_layout),

		(unsigned long long)ceph_file_layout_stripe_count(ci->i_layout),

		(unsigned long long)ceph_file_layout_object_size(ci->i_layout));

	if (ceph_file_layout_pg_preferred(ci->i_layout))

		ret += snprintf(val + ret, size, "preferred_osd=%lld\n",

			    (unsigned long long)ceph_file_layout_pg_preferred(

				    ci->i_layout));

	return ret;

}

static struct ceph_vxattr_cb ceph_file_vxattrs[] = {