selftests: mlxsw: Test VRF MAC vetoing

Test that it is possible to set an IP address on a VRF and that it is
not vetoed.

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