Bugfix/service request refactor size check (#553)

* refactor service requests from service header

* add APDU size checking and length feature

* add unit tests to check for length when passing NULL buffer

---------

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

src/bacnet/event.h

@@ -227,6 +227,12 @@ extern "C" {
         uint8_t * apdu,
         BACNET_EVENT_NOTIFICATION_DATA * data);
 
+    BACNET_STACK_EXPORT
+    size_t event_notification_service_request_encode(
+        uint8_t *apdu, 
+        size_t apdu_size, 
+        BACNET_EVENT_NOTIFICATION_DATA *data);
+
 /***************************************************
 **
 ** Decodes the service data part of Event Notification