switchdev: Adding MDB entry offload

Define HW multicast entry: MAC and VID.
Using a MAC address simplifies support for both IPV4 and IPv6.

Signed-off-by: Elad Raz <eladr@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>