net/mlx5: move header modify allocator to ipool

net/mlx5: move header modify allocator to ipool

Modify header actions are allocated by mlx5_malloc which has a big
overhead of memory and allocation time.

One of the action types under the modify header object is SET_TAG,

The SET_TAG action is commonly not reused by the flows and each flow has
its own value.

Hence, the mlx5_malloc becomes a bottleneck in flow insertion rate in
the common cases of SET_TAG.

Use ipool allocator for SET_TAG action.

Ipool allocator has less overhead of memory and insertion rate and has
better synchronization mechanism in multithread cases.

Different ipool is created for each optional size of modify header
handler.

Signed-off-by: Matan Azrad <matan@nvidia.com>
Acked-by: Suanming Mou <suanmingm@nvidia.com>