Huawei E3372 support

BEWARE: This modem will need a mode switch before you can connect, this can be done using VintageNet's power management functionality like this:

  config :vintage_net, power_managers: [{VintageNetMobile.Modem.HuaweiE3372.Modeswitch, ifname: "ppp0"}]

With this in your configuration you can now do the following to connect with the modem:

  VintageNet.configure("ppp0", %{
    type: VintageNetMobile,
    vintage_net_mobile: %{
      modem: VintageNetMobile.Modem.HuaweiE3372,
      service_providers: [%{apn: "some apn"}]
    }
  })

BEWARE Currently none of the Signal, Cell and Modem monitors are working.