Fix below compiler warning:
net/xfrm/xfrm_policy.c:1644:12: warning: ‘xfrm_dst_alloc_copy’ defined but not used [-Wunused-function]
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
        goto out;
 }
 
+#ifdef CONFIG_XFRM_SUB_POLICY
 static int xfrm_dst_alloc_copy(void **target, const void *src, int size)
 {
        if (!*target) {
        memcpy(*target, src, size);
        return 0;
 }
+#endif
 
 static int xfrm_dst_update_parent(struct dst_entry *dst,
                                  const struct xfrm_selector *sel)