net: remove NET_RX_BAD and NET_RX_CN* defines

almost no users in the tree; and the few that use them treat them
like NET_RX_DROP.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/decnet/dn_route.c

@@ -774,7 +774,7 @@ static int dn_rt_bug(struct sk_buff *skb)
 
 	kfree_skb(skb);
 
-	return NET_RX_BAD;
+	return NET_RX_DROP;
 }
 
 static int dn_rt_set_next_hop(struct dn_route *rt, struct dn_fib_res *res)