[ltp] modem driver from Smartlink

[Rob Mayoff]

+---------- On Mar 1, Tino Keitel said:
> Finally, I got it working. The only strange issue is a CPU load of ~50%
> for approx. 30 seconds periodically every few minutes while the modem
> is online.

Perhaps the modem is retraining.  The "AT#UD" command should give you a
bunch of cryptic information about the last call.  Keys 31-33 in the
output should tell you about any retrains that happened.  The manual can
be found here:

<http://www.smlink.com/support/Smart%20Link%20Modems%20AT%20Commands%2016-JAN-02.pdf>,