pckbd volume keys (part 2): knob to pass keystrokes

this diff applies on top of the previous one; it adds the hw.kbdvolume sysctl(1) entry to select how pckbd ukbd volume keys are handled: hw.kbdvolume=0 pass keystrokes to upper layer as we do for regular keys, thus usable by X apps as hot-keys or whatever. hw.kbdvolume=1

Re: pckbd volume keys (part 2): knob to pass keystrokes

this diff applies on top of the previous one; it adds the hw.kbdvolume sysctl(1) entry to select how pckbd ukbd volume keys are handled: hw.kbdvolume=0 pass keystrokes to upper layer as we do for regular keys, thus usable by X apps as hot-keys or whatever. hw.kbdvolume=1