I'm on CoreOS stable (1010.6.0).
Whenever I reboot the droplet, I always get this error message:

Failed Units: 1
    docker-tcp.socket

Then if I issue:

journalctl -b -u docker-tcp.socket
-- Logs begin at Fri 2016-06-17 18:51:06 UTC, end at Fri 2016-07-08 06:42:55 UTC. --
Jul 08 06:33:24 coreos-512mb-nyc2-01 systemd[1]: docker-tcp.socket: Failed to listen on sockets: Cannot assign requested address
Jul 08 06:33:24 coreos-512mb-nyc2-01 systemd[1]: Failed to listen on Docker Socket for the API.
Jul 08 06:33:24 coreos-512mb-nyc2-01 systemd[1]: docker-tcp.socket: Unit entered failed state.
Jul 08 06:33:24 coreos-512mb-nyc2-01 systemd[1]: docker-tcp.socket: Failed to listen on sockets: Cannot assign requested address
Jul 08 06:33:24 coreos-512mb-nyc2-01 systemd[1]: Failed to listen on Docker Socket for the API.

I followed the procedure to enable the docker-tcp socket here:
https://coreos.com/os/docs/latest/customizing-docker.html

For now, if I stop docker.service manually, and start docker-tcp.socket first, then I can start docker.service without any problem. But, I must do this after each reboot, which is not terrible.

I would like to fix this error, so that my droplet boots correctly (and the docker-tcp.socket gets started without any error).

Here's my docker-tcp.socket:

[Unit]
Description=Docker Socket for the API
Before=docker.service

[Socket]
ListenStream=172.17.0.1:2375
BindIPv6Only=both
Service=docker.service

[Install]
WantedBy=sockets.target

Here's my docker.service:

[Unit]
Description=Docker Application Container Engine
Documentation=http://docs.docker.com
After=docker.socket early-docker.target network.target
Requires=docker.socket early-docker.target

[Service]
Environment="DOCKER_CGROUPS=--exec-opt native.cgroupdriver=systemd"
EnvironmentFile=-/run/flannel_docker_opts.env
MountFlags=slave
LimitNOFILE=1048576
LimitNPROC=1048576
ExecStart=/usr/lib/coreos/dockerd daemon --host=fd:// --insecure-registry 0.0.0.0:5000 $DOCKER_OPTS $DOCKER_CGROUPS $DOCKER_OPT_BIP $DOCKER_OPT_MTU $DOCKER_OPT_IPMASQ

[Install]
WantedBy=multi-user.target

What's wrong with my setup, and how would I ensure that docker-tcp.service gets loaded before docker.service?