freetdm: move queue dtmf to the private core

libs/freetdm/src/include/private/ftdm_core.h

@@ -547,6 +547,18 @@ FT_DECLARE(ftdm_status_t) ftdm_channel_open_chan(ftdm_channel_t *ftdmchan);
  */
 FT_DECLARE(ftdm_status_t) ftdm_span_next_event(ftdm_span_t *span, ftdm_event_t **event);
 
+/*! 
+ * \brief Enqueue a DTMF string into the channel
+ *
+ * \param ftdmchan The channel to enqueue the dtmf string to
+ * \param dtmf null-terminated DTMF string
+ *
+ * \retval FTDM_SUCCESS success
+ * \retval FTDM_FAIL failure
+ */
+FT_DECLARE(ftdm_status_t) ftdm_channel_queue_dtmf(ftdm_channel_t *ftdmchan, const char *dtmf);
+
+
 /*!
   \brief Assert condition
 */