[NETNS][DCCPV6]: Don't pass NULL to ip6_dst_lookup.

This call uses the sock to get the net to lookup the routing
in. With CONFIG_NET_NS this code will OOPS, since the sk ptr
is NULL.

After looking inside the ip6_dst_lookup and drawing the analogy
with respective ipv6 code, it seems, that the dccp ctl socket 
is a good candidate for the first argument.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Acked-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dccp/ipv6.c

@@ -322,7 +322,7 @@ static void dccp_v6_ctl_send_reset(struct sock *sk, struct sk_buff *rxskb)
 	security_skb_classify_flow(rxskb, &fl);
 
 	/* sk = NULL, but it is safe for now. RST socket required. */
-	if (!ip6_dst_lookup(NULL, &skb->dst, &fl)) {
+	if (!ip6_dst_lookup(dccp_v6_ctl_sk, &skb->dst, &fl)) {
 		if (xfrm_lookup(&skb->dst, &fl, NULL, 0) >= 0) {
 			ip6_xmit(dccp_v6_ctl_sk, skb, &fl, NULL, 0);
 			DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);