CONFIG_USB_U_AUDIO (not configurable)

modulename: u_audio.ko

configname: CONFIG_USB_U_AUDIO

Linux Kernel Configuration
└─>Device Drivers
└─>USB support
└─>USB Gadget Support
└─>USB_U_AUDIO
In linux kernel since version 4.2 (release Date: 2015-08-30)  
source code:
drivers/usb/gadget/function//u_audio.c