This is the mentioned userspace tool. Build with:
cc -o batnl batnl.c $(pkg-config --cflags --libs libnl-1) -Wall
It uses the outdated libnl-1 instead of the current libnl-3 API to be compatible with OpenWrt's libnl-tiny.
It is only a quick-and-dirty example for the usage of the GENL API, so it doesn't check for a lot of errors...
Regards, Matthias