net/mlx5e: Add cache for HW modify header IDs

Packets belonging to flows which are different by matching may still need
to go through the same header re-write. Add a cache for header re-write IDs
keyed by the binary chain of modify header actions.

The caching is supported for both eswitch and NIC use-cases, where the
actual conversion of the code to use caching comes in next patches, one
per use-case.

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