Add a function libnet_conf_get_seqnum() to the libnet_conf API.

This is to provide a change sequence number to users, so that they
can use it to detect change in the config and trigger a reload.

Michael
(This used to be commit a0b12f4d815fa92c8826954e6d73546c8a751583)

source3/libnet/libnet_conf.c

@@ -481,6 +481,19 @@ void libnet_conf_close(struct libnet_conf_ctx *ctx)
 	TALLOC_FREE(ctx);
 }
 
+/**
+ * Get the change sequence number of the given service/parameter.
+ *
+ * NOTE: Currently, for registry configuration, this is independent
+ * of the service and parameter, it returns the registry-sequence
+ * number.
+ */
+uint64_t libnet_conf_get_seqnum(struct libnet_conf_ctx *ctx,
+				const char *service, const char *param)
+{
+	return (uint64_t)regdb_get_seqnum();
+}
+
 /**
  * Drop the whole configuration (restarting empty).
  */