Quectel EC21-V modem not showing the right registering state

[Alfonso Sanchez-Beato]

Hi,

I found that a Quectel EC21-V modem was not showing the right state.
This is an LTE-only modem, so the only supported network is EPS, but
mm-broadband-modem-qmi.c was never calling
mm_iface_modem_3gpp_update_eps_registration_state(), so the modem
state never changed. This patch makes MM show the right status:

https://paste.ubuntu.com/=7Stv2xjCKm/

But I am not sure if this is the right approach, so I am sending this
for comments.

This is what I see with qmiclient:

$ qmicli -d /dev/cdc-wdm0 --nas-get-serving-system
[/dev/cdc-wdm0] Successfully got serving system:
        Registration state: 'registered'
        CS: 'detached'
        PS: 'attached'
        Selected network: '3gpp'
        Radio interfaces: '1'
                [0]: 'lte'
        Roaming status: 'off'
        Data service capabilities: '1'
                [0]: 'lte'
        Current PLMN:
                MCC: '311'
                MNC: '480'
                Description: 'V� '
        Roaming indicators: '1'
                [0]: 'off' (lte)
        3GPP time zone offset: '-300' minutes
        3GPP daylight saving time adjustment: '0' hours
        3GPP location area code: '65534'
        3GPP cell ID: '15769377'
        Detailed status:
                Status: 'available'
                Capability: 'ps'
                HDR Status: 'none'
                HDR Hybrid: 'no'
                Forbidden: 'no'
        LTE tracking area code: '15620'
        Full operator code info:
                MCC: '311'
                MNC: '480'
                MNC with PCS digit: 'yes'

Thanks,
Alfonso