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/include/net/genetlink.h b/include/net/genetlink.h
index decdda5..747c255 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -162,9 +162,9 @@
  * @skb: socket buffer the message is stored in
  * @hdr: generic netlink message header
  */
-static inline int genlmsg_cancel(struct sk_buff *skb, void *hdr)
+static inline void genlmsg_cancel(struct sk_buff *skb, void *hdr)
 {
-	return nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
+	nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
 }
 
 /**