net/mlx5e: Fix matching on modified inner ip_ecn bits

Tunnel device follows RFC 6040, and during decapsulation inner
ip_ecn might change depending on inner and outer ip_ecn as follows:

 +---------+----------------------------------------+
 |Arriving |         Arriving Outer Header          |
 |   Inner +---------+---------+---------+----------+
 |  Header | Not-ECT | ECT(0)  | ECT(1)  |   CE     |
 +---------+---------+---------+---------+----------+
 | Not-ECT | Not-ECT | Not-ECT | Not-ECT | <drop>   |
 |  ECT(0) |  ECT(0) | ECT(0)  | ECT(1)  |   CE*    |
 |  ECT(1) |  ECT(1) | ECT(1)  | ECT(1)* |   CE*    |
 |    CE   |   CE    |  CE     | CE      |   CE     |
 +---------+---------+---------+---------+----------+

Cells marked above are changed from original inner packet ip_ecn value.

Tc then matches on the modified inner ip_ecn, but hw offload which
matches the inner ip_ecn value before decap, will fail.

Fix that by mapping all the cases of outer and inner ip_ecn matching,
and only supporting cases where we know inner wouldn't be changed by
decap, or in the outer ip_ecn=CE case, inner ip_ecn didn't matter.

Fixes: bcef735c ("net/mlx5e: Offload TC matching on tos/ttl for ip tunnels")
Signed-off-by: Paul Blakey <paulb@nvidia.com>
Reviewed-by: Oz Shlomo <ozsh@nvidia.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>