test/compress: fix missing include

Build of test_compressdev.c fails on FreeBSD due to the missing
include of unistd.h, to provide the function usleep.

Fixes: b06aa643ca ("test/compress: add initial unit tests")
Cc: stable@dpdk.org

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>

app/test/test_compressdev.c

@@ -5,6 +5,7 @@
 #include <zlib.h>
 #include <math.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #include <rte_cycles.h>
 #include <rte_malloc.h>