Added ModifySubscriptions Service.

src/server/ua_services.h

@@ -262,6 +262,10 @@ void Service_CreateSubscription(UA_Server *server, UA_Session *session,
                                 const UA_CreateSubscriptionRequest *request,
                                 UA_CreateSubscriptionResponse *response);
 
+void Service_ModifySubscription(UA_Server *server, UA_Session *session,
+                                const UA_ModifySubscriptionRequest *request,
+                                UA_ModifySubscriptionResponse *response);
+
 void Service_DeleteSubscriptions(UA_Server *server, UA_Session *session,
                                  const UA_DeleteSubscriptionsRequest *request,
                                  UA_DeleteSubscriptionsResponse *response);