Add a sysctl entry for the evdev device number (devnum) to allow libudev-devd to
populate the corresponding device information fields (MAJOR and MINOR) when
running in a jail with no input devices exposed through devfs.
Signed-off-by: Quentin Thébault <quentin.thebault@defenso.fr>
Sponsored by: Defenso
MFC after: 3 days