Logging functionality that used to be part of mms-engine has been
migrated to libglibutil

ligofono 1.0.11 does it for us.

This error means that operation should be retried.

It's not being used at the moment but we may need it soon.

The default should be IMSI of the SIM associated with the
default voice modem (if it's not empty)

We need to use org.nemomobile.ofono.ModemManager API to notify ofono
that we need to download MMS so that it enables mobile data for the
appropriate SIM. If it's different from the currently selected data SIM,
then connman will be prevented from using mobile data while MMS download
is taking place.