+ * Tries to deserialize a socket control message of a given
+ * @level and @type. This will ask all known (to GType) subclasses
+ * of #GSocketControlMessage if they can understand this kind
+ * of message and if so deserialize it into a #GSocketControlMessage.
+ *
+ * If there is no implementation for this kind of control message, %NULL
+ * will be returned.
+ *
+ * Returns: (transfer full): the deserialized message or %NULL