cinterion: Fix CDC-ECM support for ELS61-E2

This is in draft status to get some general feedback:

• i can delete the commit that contain log message changes from this mr or create a separate mr
• tested with the ELS61-E2 modem in CDC-ECM mode and IPv4 when auto connect in disabled in modem config
• the "validate connection" step is removed for the ELS61-E2 modem. Should it be re-added? If yes, how?
• I am not sure if i broke something for other modems.

When the data connection is started with AT^SWWAN, the modem expects the DHCP discover packet from the TE while the command is running, i.e. while the modem has not replied yet. In order to achieve that, the bearer is marked as connected as soon as the command is issued. This makes the NetworkManager start the DHCP process.

If the modem replies with an error, the bearer will be marked disconnected later on.

See !50 (merged) for a similar functionality in the ublox driver.

Signed-off-by: Christian Taedcke christian.taedcke@lemonbeat.com