replace memcmp on message id struct with direct compare

cset 3761122c fixed one place, but a few others remained.
This should take care of them all and fix a missing
IE in Add WLAN responses.

src/common/capwap_element.c

@@ -139,7 +139,7 @@ struct capwap_list_item* capwap_get_message_element(struct capwap_parsed_packet*
 	while (search) {
 		struct capwap_message_element_itemlist* messageelement =
 			(struct capwap_message_element_itemlist*)search->item;
-		if ((id.vendor == messageelement->id.vendor) && (id.type == messageelement->id.type))
+		if (message_element_id_eq(id, messageelement->id))
 			return search;
 
 		/* */

src/common/capwap_element.h

@@ -10,6 +10,9 @@ struct capwap_message_element_id
 	uint16_t type;
 };
 
+#define message_element_id_eq(a, b)			\
+	(((a).vendor == (b).vendor) && ((a).type == (b).type))
+
 /* */
 typedef void* capwap_message_elements_handle;
 struct capwap_write_message_elements_ops {