Add an osmocom watchdog

[supersat]

If an osmocom packet between the phones is ever dropped (i.e., if the cable becomes momentarily loose), cell_log will lock up waiting for a response from layer1, and layer1 will lock up waiting for a command from cell_log. This should be detected with some sort of timeout and restart cell_log. If a few restart attempts aren't successful, then logging should be turned off and a high priority notification shown to alert the user that the connection between the phones has stopped working.