Everthing is working, lets wrap up:
In /etc/pve/lxc/{{ VMID }}.conf add:
lxc.mount.entry: /dev/net dev/net none bind,create=dir
lxc.mount.entry: /tmp/net-cls-v1 tmp/net-cls-v1 none bind,create=dir
On your Proxmox host do:
script=/root/pepare-mullvad-lxc.sh
servicename=pepare-mullvad-lxc...