Currently, we can only give IP address of freeradius server allowed to interact with openwisp-radius by using the OPENWISP_RADIUS_FREERADIUS_ALLOWED_HOSTS option but this is not sufficient if the IP is not fixed, example in docker-openwisp, the IP address can be in range "172.18.0.0/16".

Hence, we need to allow user to enter IP range as well.