unregister_netdevice: waiting for eth0 to become free. Usage count = 1

Bumped into this error while removing a veth link on a Docker container recently. It doesn't look like there's a fix for this but I was able to workaround it by putting the link in promiscuous mode before removing it:

# ip link set eth0 promisc on
# ip link delete eth0 type veth

There are reports that this doesn't always work, so YMMV.