Reason for revert:
Fix RtpStreamReceiver to not recover RTX packets with incorrect SSRC.
Original issue's description:
> Revert of Only compare sequence numbers from the same SSRC in ForwardErrorCorrection. (patchset #5 id:120001 of https://codereview.webrtc.org/2893293003/ )
>
> Reason for revert:
> Breaks fuzzer.
>
> Original issue's description:
> > Only compare sequence numbers from the same SSRC in ForwardErrorCorrection.
> >
> > Prior to this CL, the ForwardErrorCorrection state would be reset whenever
> > the difference in sequence numbers of the last recovered media packet
> > and the new packet (media or FEC) was too large. This comparison did not
> > take into account that FlexFEC uses a different SSRC for the FEC packets,
> > meaning that the the state would be reset very frequently when FlexFEC
> > is used. This should not have led to any major problems, except for a
> > decreased decoding efficiency.
> >
> > This CL verifies that whenever we compare sequence numbers in
> > ForwardErrorCorrection, they do indeed belong to the same SSRC.
> >
> > BUG=webrtc:5654
> >
> > Review-Url: https://codereview.webrtc.org/2893293003
> > Cr-Commit-Position: refs/heads/master@{#18399}
> > Committed: 1476a9d789
>
> TBR=stefan@webrtc.org,holmer@google.com
> # Not skipping CQ checks because original CL landed more than 1 days ago.
> BUG=webrtc:5654
>
> Review-Url: https://codereview.webrtc.org/2919313005
> Cr-Commit-Position: refs/heads/master@{#18446}
> Committed: 92732ecc5cR=stefan@webrtc.org
BUG=webrtc:5654
Review-Url: https://codereview.webrtc.org/2918333002
Cr-Commit-Position: refs/heads/master@{#18827}
