Populate sdp_fmtp_line and channels of RTCCodecStats

Change RtpCodecCapability::parameters and RtpCodecParameters::parameters
to map from unordered_map to get welldefined FMTP lines.

Bug: webrtc:7061
Change-Id: Ie61f76bbab915d72369e36e3f40ea11838827940
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168190
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Johannes Kron <kron@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30512}

pc/rtp_parameters_conversion.cc

diff --git a/pc/rtp_parameters_conversion.cc b/pc/rtp_parameters_conversion.cc
index 93f28f1..9c7a337 100644
--- a/pc/rtp_parameters_conversion.cc
+++ b/pc/rtp_parameters_conversion.cc
@@ -164,7 +164,7 @@
     }
     cricket_codec.AddFeedbackParam(result.MoveValue());
   }
-  cricket_codec.params.insert(codec.parameters.begin(), codec.parameters.end());
+  cricket_codec.params = codec.parameters;
   return std::move(cricket_codec);
 }
 
@@ -366,8 +366,7 @@
     }
   }
   ToRtpCodecParametersTypeSpecific(cricket_codec, &codec_param);
-  codec_param.parameters.insert(cricket_codec.params.begin(),
-                                cricket_codec.params.end());
+  codec_param.parameters = cricket_codec.params;
   return codec_param;
 }