mod_skinny: remove unknown field from access_status

Cisco 7925g send access status message with just 8 byte of payload data.
Since we don't interpret the unknown 3rd field anyway, remove it. This
will prevent the first register to fail.
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Nathan Neulinger <nneul@neulinger.org>

src/mod/endpoints/mod_skinny/skinny_protocol.h

@@ -458,7 +458,7 @@ struct PACKED dialed_phone_book_message {
 struct PACKED accessory_status_message {
 	uint32_t accessory_id;
 	uint32_t accessory_status;
-	uint32_t unknown;
+	/* uint32_t unknown; */ /* this field is missing in 7925G */
 };
 
 /* RegisterAckMessage */