net/mlx5e: Ignore attempts to offload multiple times a TC flow

For VF->VF and uplink->VF rules, the TC core (cls_api) attempts
to offload the same flow multiple times into the driver, b/c we
registered to the egdev callback.

Use the flow cookie to ignore attempts to add such flows, we can't
reject them (return error), b/c this will fail the offload attempt,
so we ignore that. We indentify wrong stat/del calls using the flow
ingress/egress flags, here we do return error to the core.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Paul Blakey <paulb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>