I've had a case of a machine where eth0 was appearing a bit later
after the boot, and appearing _downed_. ifplugd then fails to detect
"link up". Thus, depending on how service startup
("ip link set dev eth0 up") races with driver initialization,
ethernet randomly fails to initialize on boot.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>