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/core/rtnetlink.c b/net/core/rtnetlink.c
index cf857c4..a9a7721 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -498,7 +498,8 @@
 	return nla_nest_end(skb, mx);
 
 nla_put_failure:
-	return nla_nest_cancel(skb, mx);
+	nla_nest_cancel(skb, mx);
+	return -EMSGSIZE;
 }
 
 int rtnl_put_cacheinfo(struct sk_buff *skb, struct dst_entry *dst, u32 id,