CONFIG_USB_F_SUBSET (not configurable)

modulename: usb_f_ecm_subset.ko

configname: CONFIG_USB_F_SUBSET

Linux Kernel Configuration
└─>Device Drivers
└─>USB support
└─>USB Gadget Support
└─>USB_F_SUBSET
In linux kernel since version 3.11 (release Date: 2013-09-02)  
source code:
drivers/usb/gadget/function//