tools/lib/: added driver selection and driver-specific parameters to backend

- atrf.c (atrf_open, select_driver, do_atrf_open): added infrastructure
  for passing the driver name and further parameters to atrf_open
- atrf.c (struct atrf_dsc): made "driver" constant
- driver.h (struct atrf_driver), atben.c (atben_open), atusb.c
  (atusb_open): added string argument to the "open" function
- atusb.c (atusb_driver): corrected unterminated comment

tools/lib/atben.c

@@ -183,7 +183,7 @@ static void atben_reset_rf(void *handle)
 }
 
 
-static void *atben_open(void)
+static void *atben_open(const char *arg)
 {
 	struct atben_dsc *dsc;