Previously, a few operations (like disable) could trigger a modem
flash in parallel with another flash. That's wrong, don't allow
that. At the same time, add in finer-grained error checking on
serial port speed operations, and fix a GSM generic bug that would
send the POWER_UP string on disable.
So many modems just don't implement carrier detect that it makes
the previous 'connected' logic useless, so base it off connect/disconnect
and fix up a few places that didn't check connect status before
trying to send commands. Also ensure the serial port is unlocked
for PPP to use when connected.
ZTE modems need to use udev rules to assign port type hints,
so generalize that and port all the plugins over to suggested
port types in the MMModem interface's grab_port() function.
Allow plugins to perform asynchronous port detection, and to defer port detection
until later. This moves the prober bits into MMPluginBase so that all plugins
can take adavantage of it only when needed; the probing is not done at udev time.
Furthermore, plugins like Novatel can flip the secondary ports over the AT mode
through deferred detection, by deferring the secondary ports until the main port
has been detected and AT$NWDMAT has been sent.
This commit also finishes the port of the rest of the plugins (except mbm) over
to the new port detection methods and plugin API.
