Instead of trying to stuff everything into the mode bitfield it
turns out it's just easier, clearer, and simpler to use different
values for each of the following:
1) the device's supported access technologies and allowed modes
2) the device's current access technology
3) the device's allowed mode preference
Since none of the AccessTechnology or AllowedMode stuff has hit a
release yet, let's make sure we're doing it the right way early on.
AccessTechnology takes over half of what NetworkMode was supposed to
do, but we'll keep NetworkMode around for a while for compatibility
anyway. Create async updaters that subclasses can use to update
the access tech when they get unsolicited messages.
Aleksander Morgado
Dan Williams
Alexander Sack
Tambet Ingo