int vconn_transact(struct vconn *, struct ofpbuf *, struct ofpbuf **);
int vconn_transact_noreply(struct vconn *, struct ofpbuf *, struct ofpbuf **);
int vconn_transact_multiple_noreply(struct vconn *, struct list *requests,
int vconn_transact(struct vconn *, struct ofpbuf *, struct ofpbuf **);
int vconn_transact_noreply(struct vconn *, struct ofpbuf *, struct ofpbuf **);
int vconn_transact_multiple_noreply(struct vconn *, struct list *requests,