Implement read_settings function to get configuration for automatic
contexts. AT^SWWAN command activates PDP context unless it has been
already activated automatically, and then starts DHCP server in the
ME. So AT^SWWAN command should be run for automatic context as well
in order to obtain IP settings from the ME.
This commit also fixes the issue uncovered by the added support for
automatic contexts: as per modem specs, AT+CGACT context should not
be reused for AT^SWWAN. Though that worked for some reason when
automatic context was reactivated without proper deactivation.
Note that in both cases success code is reported to the core before
AT^SWWAN response. This is because the ME waits until DHCP negotiation
has finished before sending the "OK" or "ERROR" result code.
Some gemalto modems provide USB ethernet interfaces for data path.
Implement gprs-context driver for such modems to send data via
USB ethernet rather than fallback to PPP.