Avoid double call to set ofono's online property

On initialization a double call to set-soft was being done for the ofono device. This caused bugs LP #1392397 and #1379807.
This is exactly how we discussed elsewhere, turns out this will not work properly: user_data has to be dereferenced to be checked. This is why I suggested after that to check the error from the g_dbus_proxy_call_finish (with source_object) to see if the call was cancelled; after that, assuming it wasn't cancelled, it's more likely to be safe to check that it's a device, before you can use modem, priv, priv->proxy, or whatever else.