Use char as the level like zipflow itself

src/vmod_zipflow.c

@@ -57,14 +57,14 @@ assert_zlib(void)
 } while(0)
 #endif
 
-static int default_level = Z_DEFAULT_COMPRESSION;
+static char default_level = Z_DEFAULT_COMPRESSION;
 
 static const void *zipflow_priv = &zipflow_priv;
 
 struct zipflow_task {
 	unsigned		magic;
 #define ZIPFLOW_TASK_MAGIC	0xaa175160
-	int			level;
+	char			level;
 	VCL_STRING		name;
 	unsigned		mode;
 	uint32_t		atime, mtime;
@@ -130,7 +130,7 @@ vmod_set_level(VRT_CTX, VCL_INT level)
 	zft = get_zipflow_task(ctx);
 	if (zft == NULL)
 		return;
-	zft->level = level;
+	zft->level = (char)level;
 }
 
 VCL_VOID