Multistream specific encoder and decoder CTLs

These are convenience macros that are specific to the opus_multistream_encoder_ctl() and opus_multistream_decoder_ctl() interface.

These are convenience macros that are specific to the opus_multistream_encoder_ctl() and opus_multistream_decoder_ctl() interface.

The CTLs from Generic CTLs, Encoder related CTLs, and Decoder related CTLs may be applied to a multistream encoder or decoder as well. In addition, you may retrieve the encoder or decoder state for an specific stream via #OPUS_MULTISTREAM_GET_ENCODER_STATE or #OPUS_MULTISTREAM_GET_DECODER_STATE and apply CTLs to it individually.