move the category setting into the element ops

this prepares the element ops for decoding vendor
ies into seperate types.

It also makes sense to keep all information about a IE
in one place.

src/common/capwap_element_imageidentifier.c

@@ -88,6 +88,7 @@ static void* capwap_imageidentifier_element_parsing(capwap_message_elements_hand
 
 /* */
 struct capwap_message_elements_ops capwap_element_imageidentifier_ops = {
+	.category = CAPWAP_MESSAGE_ELEMENT_SINGLE,
 	.create = capwap_imageidentifier_element_create,
 	.parse = capwap_imageidentifier_element_parsing,
 	.clone = capwap_imageidentifier_element_clone,