+/**
+ * Set select timeout of the scheduler.
+ *
+ * \param s The scheduler.
+ * \param t The task struct of this filter.
+ *
+ * This looks at the status of the btr node of the filter. If data is available
+ * in the input queue of the filter, or if an error occurred, a minimal timeout
+ * for the next select call is requested from the scheduler. Otherwise the
+ * scheduler timeout is left unchanged.
+ */