int vconn_transact(struct vconn *, struct ofpbuf *, struct ofpbuf **);
int vconn_transact_noreply(struct vconn *, struct ofpbuf *, struct ofpbuf **);
int vconn_transact(struct vconn *, struct ofpbuf *, struct ofpbuf **);
int vconn_transact_noreply(struct vconn *, struct ofpbuf *, struct ofpbuf **);