mempool: fix corruption due to invalid handler

mempool: fix corruption due to invalid handler

When using rte_mempool_create(), the mempool handler is selected
depending on the flags given by the user:
  - multi-consumer / multi-producer
  - multi-consumer / single-producer
  - single-consumer / multi-producer
  - single-consumer / single-producer

The flags were not properly tested, resulting in the selection of sc/sp
handler if sc/mp or mc/sp was asked. This can lead to corruption or
crashes because the get/put operations are not atomic.

Fixes: 449c49b93a6b ("mempool: support handler operations")

Signed-off-by: Weiliang Luo <droidluo@gmail.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>