test/hash: fix bucket size in perf test

test/hash: fix bucket size in perf test

The bucket size was changed from 4 to 8 but the corresponding
perf test was not changed accordingly.

In the test, the bucket size and number of buckets are used
to map to the underneath rte_hash structure. They are used
to test performance of two conditions: keys in primary
buckets only and keys in both primary and secondary buckets.

Although there is no functional issue with bucket size set
to 4, it mismatches the underneath rte_hash structure,
which may affect code readability and future extension.

Fixes: 58017c98ed53 ("hash: add vectorized comparison")
Cc: stable@dpdk.org
Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>