Fix bug in VP8 transcoding:

Author: FelonEkonom

lib/boombox/webrtc.ex

@@ -193,8 +193,9 @@ defmodule Boombox.WebRTC do
       %VP8{} = vp8 when vp8_negotiated? ->
         vp8
 
-      %RemoteStream{content_format: VP8, type: :packetized} when vp8_negotiated? ->
-        VP8
+      %RemoteStream{content_format: VP8, type: :packetized} = remote_stream
+      when vp8_negotiated? ->
+        remote_stream
 
       _format when h264_negotiated? ->
         %H264{alignment: :nalu, stream_structure: :annexb}