Trunk implementation of setting an alternate RTP source.

This contains the interface by which we can let an rtp instance know
that it might start receiving audio from a new source. This is similar
in nature to revision 197588 of Asterisk 1.4.

Review: https://reviewboard.asterisk.org/r/276



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@201583 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/rtp_engine.h

@@ -323,6 +323,8 @@ struct ast_rtp_engine {
 	void (*packetization_set)(struct ast_rtp_instance *instance, struct ast_codec_pref *pref);
 	/*! Callback for setting the remote address that RTP is to be sent to */
 	void (*remote_address_set)(struct ast_rtp_instance *instance, struct sockaddr_in *sin);
+	/*! Callback for setting an alternate remote address */
+	void (*alt_remote_address_set)(struct ast_rtp_instance *instance, struct sockaddr_in *sin);
 	/*! Callback for changing DTMF mode */
 	int (*dtmf_mode_set)(struct ast_rtp_instance *instance, enum ast_rtp_dtmf_mode dtmf_mode);
 	/*! Callback for retrieving statistics */
@@ -638,6 +640,28 @@ struct ast_frame *ast_rtp_instance_read(struct ast_rtp_instance *instance, int r
  */
 int ast_rtp_instance_set_remote_address(struct ast_rtp_instance *instance, struct sockaddr_in *address);
 
+/*!
+ * \brief Set the address of an an alternate RTP address to receive from
+ *
+ * \param instance The RTP instance to change the address on
+ * \param address Address to set it to
+ *
+ * \retval 0 success
+ * \retval -1 failure
+ *
+ * Example usage:
+ *
+ * \code
+ * ast_rtp_instance_set_alt_remote_address(instance, &sin);
+ * \endcode
+ *
+ * This changes the alternate remote address that RTP will be sent to on instance to the address given in the sin
+ * structure.
+ *
+ * \since 1.6.3
+ */
+int ast_rtp_instance_set_alt_remote_address(struct ast_rtp_instance *instance, struct sockaddr_in *address);
+
 /*!
  * \brief Set the address that we are expecting to receive RTP on
  *