net/mlx5e: Don't match double-vlan packets if cvlan is not set

commit ada09af9 upstream.

Currently, match VLAN rule also matches packets that have multiple VLAN
headers. This behavior is similar to buggy flower classifier behavior that
has recently been fixed. Fix the issue by matching on
outer_second_cvlan_tag with value 0 which will cause the HW to verify the
packet doesn't contain second vlan header.

Fixes: 699e96dd ("net/mlx5e: Support offloading tc double vlan headers match")
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>