MXS-2196: Pass the SERVICE pointer when allocating a DCB

The value would otherwise be assigned outside of it and in some cases not
at all. Now all DCBs (apart from internal ones) have a valid SERVICE
pointer.

The SERV_LISTENER pointer should not be in the DCBs but in the
session. This way the listener is an attribute of a session instead of a
connection. If this is implemented, the authenticator data can be more
easily shared.

server/modules/routing/binlogrouter/blr_master.cc

@@ -186,7 +186,7 @@ static void blr_start_master(void* data)
 
     pthread_mutex_unlock(&router->lock);
 
-    DCB* client = dcb_alloc(DCB_ROLE_INTERNAL, NULL);
+    DCB* client = dcb_alloc(DCB_ROLE_INTERNAL, NULL, NULL);
 
     /* Create fake 'client' DCB */
     if (client == NULL)