Without fully analyzing what the old code https://git.sailfishos.org/mer-core-attic/statefs-providers/blob/master/src/ofono/provider_ofono.cpp#L535 did, I could guess a property Attached of some connection manager was exported to statefs under the name GPRSAttached.
Try whether
$ dbus-send --print-reply --system --dest=org.ofono /ril_0 org.ofono.ConnectionManager.GetProperties
is what you are looking for.