test/latency: fix stack smashing

test/latency: fix stack smashing

Caught in one Travis run:
 + ------------------------------------------------------- +
 + Test Suite : Latency Stats Unit Test Suite
 + ------------------------------------------------------- +
 + TestCase [ 0] : test_latency_init succeeded
 + TestCase [ 1] : test_latency_update succeeded
[snip]
 + TestCase [1601724781] : test_latencystats_get_names succeeded
[snip]
 + Tests Failed :      1601790830

htonl(1601724781) -> "m", "a", "x", "_"
htonl(1601790830) -> "n", "c", "y", "_"

Looks like someone went too far.

The test passes a bigger size than the array it passes along.

Fixes: 1e3676a06e4c ("test/latency: add unit tests for latencystats library")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Aaron Conole <aconole@redhat.com>