[core/media] allow transcoding between different rates in Opus

Fixes for issue signalwire#2226, we've found that the patch signalwire#2582 has the side effect
of causing calls that fail to negotiate the same codec as Leg A for Leg B
to fail with SIP 488 INCOMPATIBLE_DESTINATION. That's not an option for us,
we need backwards compatibility with other codecs.

Rather than apply this for all codecs it should only apply for Opus. Now
calls using Opus and other codecs establish correctly on both legs, and there
are no issues with codec negotiation when the codecs on Leg A and Leg B don't
match.

Tested-by: Jérôme Poulin <[email protected]>

Author: shaunjstokes

src/switch_core_media.c

@@ -5517,6 +5517,10 @@ SWITCH_DECLARE(uint8_t) switch_core_media_negotiate_sdp(switch_core_session_t *s
 					uint32_t bit_rate = imp->bits_per_second;
 					uint32_t codec_rate = imp->actual_samples_per_second;
 
+					if (!strcasecmp(map->rm_encoding, "opus")) {
+						codec_rate = imp->actual_samples_per_second;
+					}
+
 					if (imp->codec_type != SWITCH_CODEC_TYPE_AUDIO) {
 						continue;
 					}