Modem connection manager changes

Restart the telit connection manager after a pre-set period of time
attempting to connect to network (WAIT_WAIT_FOR_NETWORK state).

Put a limit on how many times we can try to open a PDP context before we
restart the telit state machine. This should help recover the connection
if we lose the network after we enter that step.

Reduced the socket open timeout setting from 60 seconds to 15 seconds.
Should make error recovery more responsive.

Process ERROR messages right away for commands that take a long time.
Should make error recovery more responsive.

Default linker setting changed to overwrite NVM (which includes modem
config settings) when flashing firmware.