[IPV6] NDISC: Add proxy_ndp sysctl.

We do not always need proxy NDP functionality even we
enable forwarding.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index b2be749..6671691 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -412,7 +412,9 @@
 		return -ETIMEDOUT;
 	}
 
-	if (pneigh_lookup(&nd_tbl, &hdr->daddr, skb->dev, 0)) {
+	/* XXX: idev->cnf.proxy_ndp? */
+	if (ipv6_devconf.proxy_ndp &&
+	    pneigh_lookup(&nd_tbl, &hdr->daddr, skb->dev, 0)) {
 		int proxied = ip6_forward_proxy_check(skb);
 		if (proxied > 0)
 			return ip6_input(skb);