in TUD_AUDIO_HEADSET_STEREO_DESCRIPTOR, _nitfs should be 3.
I believe that there is a mistake in the definition of TUD_AUDIO_HEADSET_STEREO_DESCRIPTOR.  The nitfs in the audio descriptor is always 3 regardless of ITF_NUM_TOTAL.
@@ -86,7 +86,7 @@ enum
#define TUD_AUDIO_HEADSET_STEREO_DESCRIPTOR(_stridx, _epout, _epin) \
/* Standard Interface Association Descriptor (IAD) */\
- TUD_AUDIO_DESC_IAD(/*_firstitfs*/ ITF_NUM_AUDIO_CONTROL, /*_nitfs*/ ITF_NUM_TOTAL, /*_stridx*/ 0x00),\
+ TUD_AUDIO_DESC_IAD(/*_firstitfs*/ ITF_NUM_AUDIO_CONTROL, /*_nitfs*/ 3, /*_stridx*/ 0x00),\
/* Standard AC Interface Descriptor(4.7.1) */\
TUD_AUDIO_DESC_STD_AC(/*_itfnum*/ ITF_NUM_AUDIO_CONTROL, /*_nEPs*/ 0x00, /*_stridx*/ _stridx),\
/* Class-Specific AC Interface Header Descriptor(4.7.2) */\
