Support muxing vp8 in ogg

[Carl Eugen Hoyos]

$ ffmpeg -i videotest.ogv -vcodec copy out.ogg
ffmpeg version N-80887-gd9e1e08 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      55. 27.100 / 55. 27.100
  libavcodec     57. 48.101 / 57. 48.101
  libavformat    57. 40.101 / 57. 40.101
  libavdevice    57.  0.102 / 57.  0.102
  libavfilter     6. 47.100 /  6. 47.100
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  1.100 /  2.  1.100
  libpostproc    54.  0.100 / 54.  0.100
[ogg @ 0x260d3c0] Broken file, keyframe not correctly marked.
Input #0, ogg, from 'videotest.ogv':
  Duration: 00:00:02.33, start: 0.000000, bitrate: 261 kb/s
    Stream #0:0: Video: vp8, yuv420p, 320x240, SAR 1:1 DAR 4:3, 30 tbr, 30 tbn, 30 tbc
[ogg @ 0x2614ac0] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
[ogg @ 0x2614ac0] Unsupported codec id in stream 0
Output #0, ogg, to 'out.ogg':
  Metadata:
    encoder         : Lavf57.40.101
    Stream #0:0: Video: vp8, yuv420p, 320x240 [SAR 1:1 DAR 4:3], q=2-31, 30 tbr, 30 tbn, 30 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument

[James]

Added in 120f34b6ac062568a395ebc9490c7d213c264087