開關touchpad的熱鍵在udev中已經標準化

commit a1ca5f60e0770299c5c5f21bd371f5823802412b
Author: Bastien Nocera 
Date:   Thu Nov 4 23:58:56 2010 +0000

    extras/keymap: Make touchpad buttons consistent
    
    We'll need to standardise on the Touchpad related keys in udev, kernel, and
    X.org. I selected F21 for XF86TouchpadToggle, F22 for XF86TouchpadOn and F23
    for XF86TouchpadOff.
    
    See:
    https://bugs.freedesktop.org/show_bug.cgi?id=31333
    
    Signed-off-by: Martin Pitt 

參考 Touchpad toggle mess

Bug 31333 - Standardise Touchpad toggling keys