rtnetlink: Remove passing of attributes into rtnl_doit functions

With decnet converted, we can finally get rid of rta_buf and its
computations around it. It also gets rid of the minimal header
length verification since all message handlers do that explicitly
anyway.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index b4b3508..5904429 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -1616,7 +1616,7 @@
 /*
  * This is called by both endnodes and routers now.
  */
-static int dn_cache_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh, void *arg)
+static int dn_cache_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh)
 {
 	struct net *net = sock_net(in_skb->sk);
 	struct rtmsg *rtm = nlmsg_data(nlh);