HP lt4120 failing to make single-stack connections on LTE using MM

[Tore Anderson]

* Aleksander Morgado

> Oh wait, this is a Intel based MBIM modem, right? If so, we need
> AT-based reset operations. I believe I still have the HPlt4120 around
> here, will try to implement that. Tracking it here:
> https://gitlab.freedesktop.org/mobile-broadband/ModemManager/issues/86

I don't really know, to be honest. I'm using qmicli to manage it and that
works (including «--dms-set-operating-mode=foo»). ModemManager says it's
MBIM, however. Is MBIM/QMI an either/or thing? It seems to me that this
modem is both.

  -------------------------
  Hardware |   manufacturer: 'HP'
           |          model: 'MBIM [03F0:9D1D]'
           |       revision: 'T77W595.F0.0.0.6.6.GC.029'
           |   H/W revision: 'HP lt4120 Snapdragon X5 LTE'
           |      supported: 'gsm-umts, lte'
           |        current: 'gsm-umts, lte'
           |   equipment id: '358894065774253'
  -------------------------
  System   |         device: '/sys/devices/pci0000:00/0000:00:14.0/usb1/1-3'
           |        drivers: 'cdc_mbim'
           |         plugin: 'Generic'
           |   primary port: 'cdc-wdm0'
           |          ports: 'cdc-wdm0 (mbim), wwp0s20f0u3c3 (net)'
  -------------------------

Tore