network permissions: implement checks

network permissions: implement checks

when creating a new container
when restoring a backup
when cloning a container
and obviously, when changing the nics of an existing container

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
 [ T: add $opt in override param check ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>