The generic CDMA superclass already checks minimal registration state,
and when some of the additional query_registration_state() subclass checks
were being performed, if the device returned an error (if it didn't support
the subclass' specific registration command like *STATE or ^SYSINFO) the
superclass' registration state checks would be thrown away.
Fix that by specifying the behavior of the subclass'
query_registration_state() methods to ignore most errors and leave the
superclass' registration state intact if a non-critical error occurs.
For QCDM devices we want most of what MMSerialPort does, but not
the AT command handling stuff since the commands and responses
aren't AT commands nor are they even strings. So convert everything
that MMSerialPort does into a GByteArray, and let MMAtSerialPort
handle the conversion to strings when necessary.
Some modems key the AT+CSS? response off their 1X state, so if the
modem has EVDO service but no 1X service, AT+CSS? will provide incorrect
registration state information and the registration checking will
end too early. Allow modems that can handle more specific registration
checking to skip the AT+CSS? part.
