[core, mod_opus] bring more fmtp params to core (offer/answer).

src/include/switch_module_interfaces.h

@@ -676,8 +676,14 @@ struct switch_codec_fmtp {
 	int bits_per_second;
 	/*! number of microseconds of media in one packet (ptime * 1000) */
 	int microseconds_per_packet;
-	/*! stereo  */
-	int stereo;
+	/*! maximum ptime in ms */
+	int max_ptime;
+	/*! minimum ptime in ms */
+	int min_ptime;
+	/*! stereo, typically bidirectional */
+	int stereo; 
+	/* sender properties (stereo) */
+	int sprop_stereo;
 	/*! private data for the codec module to store handle specific info */
 	void *private_info;