Tagging of PTP (and other slow protocol frames)
If we use tagging at the ingress port, we tag with VLAN frame all the
incoming traffic, this also concerns PTP, RSTP, etc:
1) related to other issue: we need to forward this to CPU regardless of
VLAN tag
2) not sure it's good if CPU receives this traffic with VLAN tags,
possible solution: untag all the traffic coming to CPU -> needs to
brainstormed whether this is good