netfilter: ip6table_mangle: Fix set-but-unused variables.

The variable 'flowlabel' is set but unused in ip6t_mangle_out().

The intention here was to compare this key to the header value after
mangling, and trigger a route lookup on mismatch.

Make it so.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/netfilter/ip6table_mangle.c

@@ -64,7 +64,8 @@ ip6t_mangle_out(struct sk_buff *skb, const struct net_device *out)
 	    (memcmp(&ipv6_hdr(skb)->saddr, &saddr, sizeof(saddr)) ||
 	     memcmp(&ipv6_hdr(skb)->daddr, &daddr, sizeof(daddr)) ||
 	     skb->mark != mark ||
-	     ipv6_hdr(skb)->hop_limit != hop_limit))
+	     ipv6_hdr(skb)->hop_limit != hop_limit ||
+	     flowlabel != *((u_int32_t *)ipv6_hdr(skb))))
 		return ip6_route_me_harder(skb) == 0 ? ret : NF_DROP;
 
 	return ret;