New 'u-blox' plugin (v2)

[Aleksander Morgado]

Hey Dan & everyone,

After Dan's review, I've updated the branch implementing support for
the ublox devices with the following changes:

 * +CGCONTRDP parser is generic, and now supports both formats (pre
and post TS 27.007 v9.4.0)

 * Added some additional comments to explain how the static IP
addressing is retrieved when in bridge mode. Note also that there is a
long README explaining most of the plugin details under plugins/ublox.

 * Removed logic implementing the automatic connection to the default
LTE bearer when the empty apn ("") was given.

 * Moved AT+CGACT? polling for connection status monitoring to the
generic modem object.

 * Added support for the new CSFB related registration state values.

 * Moved the AT+CESQ based extended signal interface support to the
generic modem.

 * Updated the AT+UBANDSEL? parser to use mm_parse_uint_list().

What I didn't do:

 * No specific hex-encoded operator name parsing in AT+COPS. Dan,
there is already a mm_3gpp_normalize_operator_name() call doing this
processing after mm_3gpp_parse_cops_read_response(), don't think we
should merge both.

 * I didn't do the +CFUN parsing generic, because the +CFUN state
numbers reported are mostly (except for the first 5) vendor-specific.

You can find the updated ublox plugin in the 'aleksander/ublox' branch
in the upstream git repository:
https://cgit.freedesktop.org/ModemManager/ModemManager/log/?h=aleksander/ublox

Reviews of the implementation are more than welcome.

-- 
Aleksander
https://aleksander.es