[ebtables] Add multicast drop rule to ebtables (#18064)

Adding rule to ebtables to drop multicast packets in kernel. This was
done to address a bug where NS packets were flooding ports with
duplicate packets.

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

Author: Ndancejic

files/image_config/ebtables/ebtables.filter.cfg

@@ -8,4 +8,5 @@
 -A FORWARD -d BGA -j DROP
 -A FORWARD -p ARP -j DROP
 -A FORWARD -p 802_1Q --vlan-encap ARP -j DROP
+-A FORWARD -d Multicast -j DROP