We currently pass a 'buffer_size' option to avformat in bytes.
Unfortunately, avformat/librist.c admits an option with the same name but in milliseconds.
The default values set in the UI (2 MB) go beyond the range admitted in ms (0-30 000)
so avformat issues errors.
This fix disables the option when rist protocol is detected.
Signed-off-by: pkv <pkv@obsproject.com>