Use proper log region sizing for fellow_cache_test

Fixes #42

src/fellow_cache.c

@@ -5968,7 +5968,7 @@ t_cache(const char *fn, unsigned chksum)
 	struct stvfe_tune tune[1];
 	const size_t memsz = 10 * 1024 * 1024;
 	const size_t dsksz = 100 * 1024 * 1024;
-	const size_t objsize_hint = 1 * 1024 * 1024;
+	const size_t objsize_hint = 4 * 1024;
 	struct fellow_cache_res fcr;
 	int injcount;
 	char *ptr;