Function Bela_setLineOutLevel 

pub unsafe extern "C" fn Bela_setLineOutLevel(
    channel: c_int,
    decibel: f32,
) -> c_int

\brief Set the level of the audio line out.

\b Important: do not call this function from within render(), as it does not make any guarantees on real-time performance.

\param channel The channel to set. Use a negative value to set all channels. \param decibels Level of the line output. Valid values will depend on the codec in use.

\return 0 on success, or nonzero if an error occurred.