Added allow_codec_switching parameter to RTCConfig.

Bug: webrtc:10795
Change-Id: I5507f1d801e262223bd18198c685b5fffa644b0b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157891
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29612}
diff --git a/api/peer_connection_interface.h b/api/peer_connection_interface.h
index 2b7da83..cc2fa46 100644
--- a/api/peer_connection_interface.h
+++ b/api/peer_connection_interface.h
@@ -673,6 +673,9 @@
     // Added to be able to control rollout of this feature.
     bool enable_implicit_rollback = false;
 
+    // Whether network condition based codec switching is allowed.
+    absl::optional<bool> allow_codec_switching;
+
     //
     // Don't forget to update operator== if adding something.
     //