This patch set adds a lifo stack handler to the external mempool
manager.

This patch utilises the mempool handler feature which allows the addition
of new mempool handlers to DPDK.

v5 changes:
  * Added the extra parameter requred for the test_mempool_basic()
    function, which has changed due to the user defined cache
    functionality.

v4 changes:
  * Update the test to replace the custom handler test with the
    stack handler test rather than just adding a stack handler test.
    The custom handler code is very similar to the stack handler, so
    there's no need to have both.

v3 changes:
  * Updated based on the latest version (v15) of the Mempool Handler feature

v2 changes:
  * updated based on mailing list feedback (Thanks Stephen)
  * checkpatch fixes.

David Hunt (2)
  mempool: add stack (lifo) mempool handler
  test: migrate custom handler test to stack handler