netlink: add nlmsg_consume() and use it in devlink compat

devlink_compat_running_version() sticks out when running
netdevsim tests and watching dropped skbs. Add nlmsg_consume()
for cases were we want to free a netlink skb but it is expected,
rather than a drop. af_netlink code uses consume_skb() directly,
which is fine, but some may prefer the symmetry of nlmsg_new() /
nlmsg_consume().

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: kuba-moo

include/net/netlink.h

@@ -41,7 +41,8 @@
  *   nlmsg_get_pos()			return current position in message
  *   nlmsg_trim()			trim part of message
  *   nlmsg_cancel()			cancel message construction
- *   nlmsg_free()			free a netlink message
+ *   nlmsg_consume()			free a netlink message (expected)
+ *   nlmsg_free()			free a netlink message (drop)
  *
  * Message Sending:
  *   nlmsg_multicast()			multicast message to several groups
@@ -1082,14 +1083,23 @@ static inline void nlmsg_cancel(struct sk_buff *skb, struct nlmsghdr *nlh)
 }
 
 /**
- * nlmsg_free - free a netlink message
+ * nlmsg_free - drop a netlink message
  * @skb: socket buffer of netlink message
  */
 static inline void nlmsg_free(struct sk_buff *skb)
 {
 	kfree_skb(skb);
 }
 
+/**
+ * nlmsg_consume - free a netlink message
+ * @skb: socket buffer of netlink message
+ */
+static inline void nlmsg_consume(struct sk_buff *skb)
+{
+	consume_skb(skb);
+}
+
 /**
  * nlmsg_multicast_filtered - multicast a netlink message with filter function
  * @sk: netlink socket to spread messages to

net/devlink/dev.c

@@ -1214,7 +1214,7 @@ static void __devlink_compat_running_version(struct devlink *devlink,
 		}
 	}
 free_msg:
-	nlmsg_free(msg);
+	nlmsg_consume(msg);
 }
 
 void devlink_compat_running_version(struct devlink *devlink,