Increase the SDP buffer size (again!) and also increase the temporary

Increase the SDP buffer size (again!) and also increase the temporary
buffer size of the fmtp parameter buffer. For Vorbis RT(S)P, these
contain full Vorbis headers, which can be up to 12kb each, formatted
in base64, so 16kb total. Patch required for proper Vorbis/RTP playback,
submitted as GSoC qualification task in the thread "RTP/Vorbis payload
implementation (GSoC qual task)" by Colin McQuillan m.niloc googlemail
com.

Originally committed as revision 18508 to svn://svn.ffmpeg.org/ffmpeg/trunk