helpers : add check_vnet_access

helpers : add check_vnet_access

if a tag is defined, test if user have a specific access to the vlan (or propagate from full bridge acl or zone)
if trunks is defined, we check permissions for each vlan of the trunks
if no tag, test if user have access to full bridge.

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
FG:
- conditionalize check for bridge
- make trunk to tags helper private for now

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>