mlxsw: spectrum: Only treat 802.1q packets as tagged packets

By default, the device considers both 802.1ad and 802.1q packets as tagged,
but this is not supported by the driver. It only supports VLAN and bridge
devices that use 802.1q protocol.

Instead, configure the device to only treat 802.1q packets as tagged
packets.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>