Deprecate SubscriptionState property from Modem3gpp interface

This patch set migrates the altair-lte plugin to use the Pco property instead of the SubscriptionState property of the Modem3gpp interface, and then deprecates and removes the SubscriptionState property.

Hey @benchan we don't want to break API for the next MM 1.10 release, so we should not remove the property from the DBus API or the libmm-glib methods to work with it. Instead, we should leave them in the APIs but doing nothing, and flag them as deprecated in the documentation. Once we have many more deprecated items we can go on and bump API and do a cleanup, but we shouldn't do it just for a few minor things like this.

See this commit where I did deprecate the property without removing it, maybe you could cherry-pick that logic instead? b382302e

@aleksm sgtm. It seems like we can land my first patch "altair-lte: migrate from SubscriptionState to Pco property", then follow with your deprecation patch. WDYT?

added 1 commit

• d78294b4 - api: deprecate SubscriptionState property

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@aleksm I replaced my second patch with your patch b382302e with some modifications. PTAL.

added 2 commits

• f28cbe24 - altair-lte: migrate from SubscriptionState to Pco property
• a9d98214 - api: deprecate SubscriptionState property

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resolved all discussions

I'm not allowed to rebase your branch via gitlab (I think there was an option when creating the MR to allow this?).

Anyway, it LGTM, just rebase and merge it yourself :)

added 6 commits

• a9d98214...beb1aab1 - 4 commits from branch mobile-broadband:master
• 408a2a9c - altair-lte: migrate from SubscriptionState to Pco property
• 025fcb7e - api: deprecate SubscriptionState property

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merged

Rebased and merged to master. Thanks