selftests: forwarding: router: Add test case for multicast destination MAC mismatch

Add test case to check that packets are not dropped when they need to be
routed and their multicast MAC mismatched to their multicast destination
IP.

i.e., destination IP is multicast and
	* for IPV4: DMAC !=  {01-00-5E-0 (25 bits), DIP[22:0]}
	* for IPV6: DMAC !=  {33-33-0 (16 bits), DIP[31:0]}

Signed-off-by: Amit Cohen <amitc@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>