[NETFILTER]: Fix incorrect use of skb_make_writable

http://bugzilla.kernel.org/show_bug.cgi?id=9920
The function skb_make_writable returns true or false.

Signed-off-by: Joonwoo Park <joonwpark81@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/netfilter/ebt_dnat.c b/net/bridge/netfilter/ebt_dnat.c
index e700cbf..1ec671d 100644
--- a/net/bridge/netfilter/ebt_dnat.c
+++ b/net/bridge/netfilter/ebt_dnat.c
@@ -20,7 +20,7 @@
 {
 	const struct ebt_nat_info *info = data;
 
-	if (skb_make_writable(skb, 0))
+	if (!skb_make_writable(skb, 0))
 		return NF_DROP;
 
 	memcpy(eth_hdr(skb)->h_dest, info->mac, ETH_ALEN);