This CL removes |default_recv_ssrc_| from DefaultUnsignalledSsrcHandler
and replaces it with calls to a new member function
WebRtcVideoChannel2::GetDefaultReceiveStreamSsrc. The latter checks
the |default_stream_| member on the
WebRtcVideoChannel2::WebRtcVideoReceiveStreams to know which stream
is the current default stream.
This change removes duplicate state and fixes an issue where
incoming unsignaled SSRCs would compete for being the default
receive stream.
BUG=webrtc:7725
Review-Url: https://codereview.webrtc.org/2906893002
Cr-Commit-Position: refs/heads/master@{#18314}