Zerotier Openvz zt0 issue

Apparently the issue was a "rights issue"; adding the -U option as described down below fixed it.

chmod 0666 /dev/net/tun

/lib/systemd/system/zerotier-one.service:

[Unit]
Description=ZeroTier One
After=network.target

[Service]
ExecStart=/usr/sbin/zerotier-one -U
Restart=always
KillMode=process

[Install]
`WantedBy=multi-user.target``