Comment 2 for bug 1775566

Even "netplan apply" with NO yaml file fixes it.
So running in the static networkd config (with the files I copied formerly created by netplan as outlied above).

Then with debug enabled it does:
$ networkctl list
IDX LINK TYPE OPERATIONAL SETUP
  1 lo loopback carrier unmanaged
  2 enp0s3 ether off unmanaged

$ sudo netplan --debug apply
DEBUG:no netplan generated networkd configuration exists
DEBUG:no netplan generated NM configuration exists
DEBUG:replug enp0s3: unbinding virtio0 from /sys/bus/virtio/drivers/virtio_net
DEBUG:replug enp0s3: rebinding virtio0 to /sys/bus/virtio/drivers/virtio_net

$ networkctl list
IDX LINK TYPE OPERATIONAL SETUP
  1 lo loopback carrier unmanaged
  8 enp3 ether routable configured

So I did after a reboot:
echo virtio0 | sudo tee /sys/bus/virtio/drivers/virtio_net/virtio0/driver/unbind
echo virtio0 | sudo tee /sys/bus/virtio/drivers/virtio_net/bind

$ networkctl list
IDX LINK TYPE OPERATIONAL SETUP
  6 enp3 ether routable configured

So it is working after the replug - adn this replug was the magic done by "netplan apply".
Now why this fails with just a static networkd config - I don't know.
But I'd say it is a networkd bug right?

The former event existed on boot
[ 0.726055] virtio_net virtio0 enp0s3: renamed from eth0
This is the one networkd should have picked up.
[ 481.972268] virtio_net virtio0 enp3: renamed from eth0
[ 481.983710] IPv6: ADDRCONF(NETDEV_UP): enp3: link is not ready
[ 482.976135] IPv6: ADDRCONF(NETDEV_CHANGE): enp3: link becomes ready

I don't know where/how to adress this further, but I hope the repro and debug helps to fix this.