[review] 3GPP registration logic updates and QMI NAS specific fixes

[Aleksander Morgado]

Hey,

The following MR is ready for review:
https://gitlab.freedesktop.org/mobile-broadband/ModemManager/merge_requests/124

This MR introduces some cleanups on how the registration updates are
managed, and explicitly fixes the "QMI NAS Initiate Network Register"
based implementation, which was not waiting for the registration
attempt to even start before assuming it was already done.

-- 
Aleksander
https://aleksander.es