rtnl: add helper to check if a notification is needed

Building on the rtnl_has_listeners helper, add the rtnl_notify_needed
helper to check if we can bail out early in the notification routines.
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Link: https://lore.kernel.org/r/20231208192847.714940-3-pctammela@mojatatu.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/rtnetlink.h

@@ -137,4 +137,19 @@ static inline int rtnl_has_listeners(const struct net *net, u32 group)
 	return netlink_has_listeners(rtnl, group);
 }
 
+/**
+ * rtnl_notify_needed - check if notification is needed
+ * @net: Pointer to the net namespace
+ * @nlflags: netlink ingress message flags
+ * @group: rtnl group
+ *
+ * Based on the ingress message flags and rtnl group, returns true
+ * if a notification is needed, false otherwise.
+ */
+static inline bool
+rtnl_notify_needed(const struct net *net, u16 nlflags, u32 group)
+{
+	return (nlflags & NLM_F_ECHO) || rtnl_has_listeners(net, group);
+}
+
 #endif	/* __LINUX_RTNETLINK_H */