Comment 2 for bug 1534678

I can now confirm my analysis of the bug! And I got a new and unpleaseant surprise, too.

First I compiled a version of modemmanager (1.4.10) where the wrongly returned pci-id 8068:3b34 is swapped to the correct usb-id 12d1:14c9 in "get_device_ids". This is just a hack, of course, no solution. Now the 'huawei' plugin is used instead of the 'generic' one and all seems well. Remember, the whole thing used to work in Ubuntu 15.04 and before!

But now the NetworkManager complains with an odd message:
NetworkManager[1108]: <warn> (ttyUSB2): Failed to connect 'Vodafone WebSessions': Connection requested both IPv4 and IPv6 but dual-stack addressing is unsupported by the modem.
And although it is marked as a warning, it makes a network connection impossible:
NetworkManager[1108]: <info> (ttyUSB2): device state change: prepare -> failed (reason 'modem-init-failed') [40 120 28]

Since the capabilities come from the modemmanager I still think, here is the right place to begin the repair.
(From my previous (working!) connections I do know, that IPv4 will be sufficient, but I find no way to signal this to the NetworkManager!)

Any usefull advice will be welcome. Thanks.