[DCCP] ipv6: dccp_v6_send_response() has a DST leak too.

It was copy&pasted from tcp_v6_send_synack() which has
a DST leak recently fixed by Eric W. Biederman.

So dccp_v6_send_response() needs the same fix too.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dccp/ipv6.c

@@ -468,6 +468,7 @@ static int dccp_v6_send_response(struct sock *sk, struct request_sock *req,
 done:
         if (opt && opt != np->opt)
 		sock_kfree_s(sk, opt, opt->tot_len);
+	dst_release(dst);
 	return err;
 }