net/mlx5e: Keep direct reference to mlx5_core_dev in tc ct

Keep and use a direct reference to the mlx5 core device in all of
tc_ct code instead of accessing it via a pointer to mlx5 eswitch
in order to support nic mode ct offload for VF devices that don't
have a valid eswitch pointer set.

Signed-off-by: Ariel Levkovich <lariel@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>