Allow plugins to specify that signal quality/access tech polling isn't needed

[Aleksander Morgado]

Hey,

This patch series improves the way the MMIfaceModem handles signal quality and access technology updates. The main improvement is that now plugins that implement load_access_technologies() or load_signal_quality() can return an UNSUPPORTED error to indicate that the polling isn't necessary, e.g. if they are going to get the updates via URCs.

The same polling logic is consolidated for both signal quality and access technology, which simplifies a bit how they are managed.

The implementation uses the Cinterion plugin as first example of such situation; if ^SIND psinfo is supported by the modem we'll use +CIEV URC based updates for access technology; otherwise we'll use AT^SMONG polling managed by the MMIfaceModem.

Comments?

    [PATCH 1/4] iface-modem: consolidate signal quality and access tech
    [PATCH 2/4] iface-modem: if bands, capabilities or modes change,
    [PATCH 3/4] port-serial-at: always prepend unsolicited message
    [PATCH 4/4] cinterion: use ^SIND unsolicited messages for access tech