test/mempool: fix no-huge mode

test/mempool: fix no-huge mode

Amount of locked memory for regular users is limited,
it is usually 64 KB by default.
Hitting this limit in rte_mempool_populate_anon()
resulted in not populating the mempool, and a test case failure:

    EAL: Test assert test_mempool_events line 585 failed: Failed to populate mempool empty1: Success
    test failed at test_mempool():1019
    Test Failed

Decrease the amount of mapped anonymous memory to fit the limit.
While there, make all function-local constants lowercase.

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

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