restricted broadcast configuration per port

[anarkiwi]

By default a port can broadcast/flood to any port in the same FAUCET VLAN.

It is desirable to restrict broadcasting/flooding on a per port basis.

If we set a port to restricted_broadcast: True, then it may broadcast/flood only to other ports in the same FAUCET VLAN where restricted_broadcast: False (e.g. ports where NFV servers, gateway may be running).

ARP and IPv6 ND are a special case - a port with restricted_broadcast: True, can still broadcast ARP requests and IPv6 NA/NSs.