Fix flaky mpool test.

In the worst case, this test will allocate 4 pages, skip 2 pages to
get aligned and then allocate 5 pages. This is a total of 11 which is
greater than the 10 previsouly available.

Change-Id: I3c52fc0503690708699d847b3fbc026ca304e771
diff --git a/src/mpool_test.cc b/src/mpool_test.cc
index 5cc7fe0..f4267b3 100644
--- a/src/mpool_test.cc
+++ b/src/mpool_test.cc
@@ -234,7 +234,7 @@
 {
 	struct mpool p;
 	constexpr size_t entry_size = 16;
-	constexpr size_t entries_per_chunk = 10;
+	constexpr size_t entries_per_chunk = 12;
 	constexpr size_t chunk_count = 10;
 	std::vector<std::unique_ptr<char[]>> chunks;
 	std::vector<uintptr_t> allocs;