netlink: Improve returned error codes

Make nlmsg_trim(), nlmsg_cancel(), genlmsg_cancel(), and
nla_nest_cancel() void functions.

Return -EMSGSIZE instead of -1 if the provided message buffer is not
big enough.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_gred.c b/net/sched/sch_gred.c
index 3a9d226..c89fba5 100644
--- a/net/sched/sch_gred.c
+++ b/net/sched/sch_gred.c
@@ -582,7 +582,8 @@
 	return nla_nest_end(skb, opts);
 
 nla_put_failure:
-	return nla_nest_cancel(skb, opts);
+	nla_nest_cancel(skb, opts);
+	return -EMSGSIZE;
 }
 
 static void gred_destroy(struct Qdisc *sch)