[review] Fix subscribed event list management in the mbim-proxy

[Aleksander Morgado]

Hey,

The following MR implements several fixes in the mbim-proxy, all
related to how the subscribed event lists are managed:
https://gitlab.freedesktop.org/mobile-broadband/libmbim/merge_requests/2

 * The proxy was maintaining a global merged list with all events from
all clients, but that only made sense when the system runs with a
single device. The merged lists should be per-device, not global to
all.

 * Device-reported error signals were tracked and processed
per-client. The logic is now simplified to have one single error
signal handling per-device.

 * If we suddenly find in the proxy that it returns NotOpened errors
(e.g. after a suspend/resume cycle) we must consider all non-standard
subscribed event lists as reseted. E.g. a client that subscribed to
QMI indications will need to explicitly re-subscribe. This fixes QMI
LOC management after a suspend/resume cycle.

 * We align now with the MBIM protocol w.r.t. how the standard service
indications are managed. We no longer require the clients to
explicitly register to them, as those are always enabled by default.
The internal device-level merged list now will completely ignore all
setups for basic connect services.

-- 
Aleksander
https://aleksander.es