rule_generator/rule_generator.functions: fix net rule generator

`udevadm info --run` no longer returns the correct run directory
 so we hard code it as "/run/udev/"

X-Gentoo-Bug: 475276
X-Gentoo-Bug-URL: https://bugs.gentoo.org/475276
Signed-off-by: Anthony G. Basile <blueness@gentoo.org>