Shave some bytes off struct bytes_tree

This brings it down from 120 to 112 bytes for me.

src/node.h

@@ -34,6 +34,8 @@
 struct bytes_tree {
 	unsigned		magic;
 #define BYTES_TREE_MAGIC 0x49c59d46
+	int			retval;
+
 	struct lock		tree_lock;
 	// esi_level > 1 signalling new data
 	pthread_cond_t		cond;
@@ -45,7 +47,6 @@ struct bytes_tree {
 	struct node		*end;
 	int			end_sent;
 	int			npending;
-	int			retval;
 };
 
 enum n_type {