[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: David S. Miller <davem@davemloft.net>
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index df07425..80c4d04 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -468,6 +468,7 @@
 done:
         if (opt && opt != np->opt)
 		sock_kfree_s(sk, opt, opt->tot_len);
+	dst_release(dst);
 	return err;
 }