net/mlx5e: CT: Fix memory leak in cleanup

CT entries are deleted via a workqueue from netfilter. If removing the
module before that, the rules are cleaned by the driver itself, but the
memory entries for them are not freed. Fix that.

Fixes: ac991b48 ("net/mlx5e: CT: Offload established flows")
Signed-off-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>