BUGFIX to OpLinkMini: oplinkmod needs to initialize the Callback Scheduler

OPLMini does not use Systemmod but its own system module called
oplinkmod - which did not initialize the callback scheduler. Making the
event dispatcher a callback caused it to no longer run due to the
missing callback scheduler initialization

flight/modules/OPLink/oplinkmod.c

@@ -118,6 +118,9 @@ static void systemTask(__attribute__((unused)) void *parameters)
     /* create all modules thread */
     MODULE_TASKCREATE_ALL;
 
+    /* start the delayed callback scheduler */
+    CallbackSchedulerStart();
+
     if (mallocFailed) {
         /* We failed to malloc during task creation,
          * system behaviour is undefined.  Reset and let