Floss: add AAC encoder config proto

  bool enhanced = 3;

}

message AacEncoderParam {

  // encoder config

  int32 sample_rate = 1;

  int32 channel_count = 2;

  int32 bit_rate = 3;

  // encode parameter

  int32 bit_depth = 4;

  int32 effective_frame_size = 5;

}

// union of different codec parameters

message ConfigParam {

  // This determines the codec type and whether it is an encoder or a decoder.

    // HFP MSBC use SBC parameters

    SbcEncoderParam hfp_msbc_encoder_param = 3;

    SbcDecoderParam hfp_msbc_decoder_param = 4;

    AacEncoderParam a2dp_aac_encoder_param = 5;

  }

}