Just out of curriousity:
Does the username “pi” indicate that it’s running on a Raspberry Pi?
The container starts on my x86_64 system but suffers from a different problem:
me@swarm1:~$ docker run -it --rm --cap-add=NET_ADMIN ubuntu:14.04 ip link add dummy0 type dumm
Unable to find image 'ubuntu:14.04' locally
14.04: Pulling from library/ubuntu
2e6e20c8e2e6: Extracting [=========================> ] 36.21MB/70.69MB
0551a797c01d: Download complete
2e6e20c8e2e6: Extracting [===========================================> ] 61.83MB/70.69MB
2e6e20c8e2e6: Pull complete
0551a797c01d: Pull complete
512123a864da: Pull complete
Digest: sha256:5c01e896fa6eeaa41f3509c64af668d71d06e318cfe373dabab9d61b9eaf6441
Status: Downloaded newer image for ubuntu:14.04
RTNETLINK answers: Operation not supported
I am not going to follow up on the RTNETLINK problem - as its not part of your OP and I have no use for it…