net/mlx5e: Check for needed capability for cvlan matching

If not supported show an error and return instead of trying to offload
to the hardware and fail.

Fixes: 699e96dd

 ("net/mlx5e: Support offloading tc double vlan headers match")
Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>