selftests: mlxsw: Consider VLAN-aware bridges as valid

Previous patches add the ability to work with VLAN-aware bridges and
VxLAN devices, so make sure such configuration no longer fails.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>