demux_lavf: add hack for stream-changing ogg input (internet radio)
Some internet radio streams are ogg/vorbis with a new stream for each
track (and the previous stream stops receiving data). Add a hack to
ignore the stream number in packets when input seems to match this
case; all packets will be effectively regarded as parts of the same
audio stream. This workaround can't work perfectly with current lavf
because it will keep adding streams and then hit its 20 stream
maximum; at that point playback will likely fail. Print a warning
about this problem and mention "-demuxer ogg" as a possible
workaround.
Currently there's no check that the vorbis extradata is actually
compatible between the streams.