Ok, to check it, I did this:
/etc/init.d/mosquitto stop
and then I restarted it manually with a modified config in /etc/mosquitto/mosquitto.conf containing this:
user root
port 1883
allow_anonymous true
listener 9001
protocol websockets
by doing this:
mosquitto -v -c /etc/mosquitto/mosquitto.conf
The broker replies with
Error: Websockets support not available.
which is the typical answer when the websockets function is not compiled. So, all there would be needed to do is to compile the already available option into the mqtt package. Is somebody from teltonika reading here to maybe add this feature to the roadmap?