Revise enabling of lirc protocol.

We have no way to know if an user needs to run the dreaded
"echo lirc > /sys(class/rc/rc0" command. We don't if if should be
run at all (e. g., usb-based RF devices) of it it's rc0, rc1 or
whatever.

Adds a configuration option which, if set, applies the command to
the configured device. Not nice, but the best we can do for now IMHO.