PLS-8 times out setting allowed modes to 3G

Hello!

Following up #643, we recently added a configuration option to the Meteo-40 for the SetCurrentModes D-Bus method to prevent the PLS-8 using 2G. Here in Berlin, selecting 4G instead avoids that issue entirely.

However, we have a customer in Uruguay who wants to use 3G and the new option isn't working for them, the PLS-8 continues to use 2G.

If I run the following command on a Meteo-40 or a PC here I get this error:

$ mmcli -m 0 --set-allowed-modes=3G
error: couldn't set current modes: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Serial.ResponseTimeout: Serial command timed out'

And the allowed modes are still "any". Of course, there's no 3G in Berlin, but I would still expect the command to succeed. I'm assuming the error in Uruguay is the same, but I can't say for certain.

Indeed, on an FXT003, the command does succeed, only 3G is allowed and the modem never connects (as expected). Why doesn't the PLS-8 do that?

Here's the version 1.20.0-1~bpo11+1 debug log from my PC.