[DECNET]: Fix build regressions.

Spotted by Arnaldo.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/decnet/dn_rules.c

@@ -241,12 +241,6 @@ static u32 dn_fib_rule_default_pref(void)
 	return 0;
 }
 
-static size_t dn_fib_rule_nlmsg_payload(struct fib_rule *rule)
-{
-	return nla_total_size(2) /* dst */
-	       + nla_total_size(2); /* src */
-}
-
 int dn_fib_dump_rules(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	return fib_rules_dump(skb, cb, AF_DECnet);