mempool: fix non-IO flag inference

mempool: fix non-IO flag inference

When mempool had been created with RTE_MEMPOOL_F_NO_IOVA_CONTIG flag
but later populated with valid IOVA, RTE_MEMPOOL_F_NON_IO was unset,
while it should be kept. The unit test did not catch this
because rte_mempool_populate_default() it used was populating
with RTE_BAD_IOVA.

Keep setting RTE_MEMPOOL_NON_IO at an empty mempool creation
and add an assert for it in the unit test (remove the separate case).
Do not reset the flag if RTE_MEMPOOL_F_ON_IOVA_CONTIG is set.

Fixes: 11541c5c81dd ("mempool: add non-IO flag")

Signed-off-by: Dmitry Kozlyuk <dkozlyuk@nvidia.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>