How to update AREDN config files

1) do (or start) an AREDN build, e.g. "make MAINTARGET=ipq40xx SUBTARGET=mikrotik"
2) from ./openwrt directory, "make menuconfig"
3) update config options via the menu and save
4) capture the updated config, from ./openwrt directory, e.g.:
    "./scripts/diffconfig.sh > ../configs/ipq40xx-mikrotik.config"

Notes:
1) adding the same option to every MAINTARGET-SUBTARGET.config file is
    done one at a time.
2) It can be very difficult to manually determine compatible dependencies
    of config options.
3) Not recommended to manually update the MAINTARGET-SUBTARGET.config
    file.  If you do, append the setting at the end (will take 
    precendent).