[mod_opus] configure timestamp increments to be fixed

Allow transcoding between different rate without messing up the
RTP timestamps after transcoding kicks-in.

@celliso1: It appears this PR (#2623) has revealed a bug in the opus encoder affecting the timestamp increment. The RFC 7587 states opus always increments at 48kHz regardless of the payload sample rate, but mod_opus.c is using 16 kHz or 8kHz samples per packet.

Co-authored-by: celliso1 <celliso1@users.noreply.github.com>
Tested-by: Jérôme Poulin <jeromepoulin@gmail.com>

Author: ticpu

src/mod/codecs/mod_opus/mod_opus.c

@@ -1487,7 +1487,7 @@ SWITCH_MODULE_LOAD_FUNCTION(mod_opus_load)
 	}
 
 	/* 16 khz */
-	samples = 160;
+	samples = 480;
 	bytes = 320;
 	mss = 10000;
 	rate = 16000;
@@ -1584,7 +1584,7 @@ SWITCH_MODULE_LOAD_FUNCTION(mod_opus_load)
 	}
 
 	/* 8 khz */
-	samples = 80;
+	samples = 480;
 	bytes = 160;
 	mss = 10000;
 	rate = 8000;