Enable fails for QUALCOMM modem with MM 1.20.4

[Aleksander Morgado]

Hey!

> From a quick look at src/mm-broadband-modem-qmi.c ModemManager now seems to
> use DMSSetEventReport to enable indications for OperatingMode which is not
> supported by older devices.
>

We should never break support for older devices, at least that is the
target! If anyone ever sees a modem that used to work and now it
doesn't, please report it.
For this particular issue, the fix to ignore this MissingArgument
error went in commit 6006dd1d63, which it looks like only exists in
1.22, it was never backported to 1.20.x

-- 
Aleksander