This, while being slightly unsystematic, reduces the risk of confusing
"1" (one) and "l" (lower-case ell).
- tools/atrf-gpio/atben.c (do_atben), tools/atrf-gpio/atusb.c
(do_atusb): treat 'o' as an alias of 'l'
- tools/atrf-gpio/atrf-gpio.c (usage): list 'o' as alternative for 'l'