Refer to scheduler via hydra and not charon.

src/libcharon/sa/tasks/child_rekey.c

@@ -330,7 +330,7 @@ static status_t process_i(private_child_rekey_t *this, message_t *message)
 			DBG1(DBG_IKE, "CHILD_SA rekeying failed, "
 								"trying again in %d seconds", retry);
 			this->child_sa->set_state(this->child_sa, CHILD_INSTALLED);
-			charon->scheduler->schedule_job(charon->scheduler, job, retry);
+			hydra->scheduler->schedule_job(hydra->scheduler, job, retry);
 		}
 		return SUCCESS;
 	}