VLAN: filter multicast and client-to-client unicast traffic

VLAN: filter multicast and client-to-client unicast traffic

With this change, client-to-client communications are possible only if
clients were configured with the same PVID.

At the same time also broadcast packets are now forwarded only to hosts
belonging to the originator VLAN.

Signed-off-by: Fabian Knittel <fabian.knittel@lettink.de>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20191009143422.9419-5-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg18922.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>