modemmanager: set allowedmode to 'any' if nothing is configured

modemmanager: set allowedmode to 'any' if nothing is configured

The modem saves the permitted technology configuration in the modem
itself. If the technology configuration is deleted in the uci, this is
not passed on to the modem. This means that the previously saved
technology configuration is remains in the modem and is therefore still
active. By setting the technology to 'any', if no option is set, all
technologies are allowed again.

Signed-off-by: Florian Eckert <redacted>