openbench-logic-sniffer: Avoid recreating event source

With the current driver API and the corresponding session event
handling, it is not possible to destroy and then re-create an
event source with the same key within the same main loop iteration.

The next generation driver API will fix this problem. But for now,
just change the driver to make do without that sort of thing. Also
increase the I/O timeout to 100 ms to be safer in the event of all
kind of delays the OS environment may induce.

This fixes bug #678.