default or selected kernelversion does not have config value CONFIG_USB_U_RNDIS.
Result is shown for kernelversion 6.5.1

CONFIG_USB_U_RNDIS (not configurable)

modulename: u_rndis.ko

configname: CONFIG_USB_U_RNDIS

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