discover/udev: Don't call udev_set_log_fn()

As of libudev 218 udev_set_log_fn() is deprecated, causing a
-Wdeprecated-declarations warning when building, and is otherwise a
noop.
Add a configure check for libudev, and only call udev_set_log_fn() if
using a version older than 218.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>