* Refactored kill_all to first try to TERM all pids, then use KILL on pids taking too long to exit.
* Only kill pids that currently have /dev/ttyS1 open.
* Skip the 100ms sleep if no process has /dev/ttyS1 open.
My unconfigured WLAN dongle has a self-assigned I, while my ethernet has a valid address. In this scenario, it breaks PPP mode. The change filters this address range and resolves the problem for me.