Apply by doing:
cd /usr/src
patch -p0 < 001_pflow.patch
Then build and install a new kernel.
Index: sys/net/if_pflow.c
===================================================================
RCS file: /vol/openbsd/cvs/src/sys/net/if_pflow.c,v
retrieving revision 1.32
diff -u -p -r1.32 if_pflow.c
--- sys/net/if_pflow.c 5 Jul 2013 17:14:27 -0000 1.32
+++ sys/net/if_pflow.c 7 Nov 2013 16:48:45 -0000
@@ -269,6 +269,12 @@ pflow_clone_destroy(struct ifnet *ifp)
int s;
s = splnet();
+ if (timeout_initialized(&sc->sc_tmo))
+ timeout_del(&sc->sc_tmo);
+ if (timeout_initialized(&sc->sc_tmo6))
+ timeout_del(&sc->sc_tmo6);
+ if (timeout_initialized(&sc->sc_tmo_tmpl))
+ timeout_del(&sc->sc_tmo_tmpl);
pflow_flush(sc);
if_detach(ifp);
SLIST_REMOVE(&pflowif_list, sc, pflow_softc, sc_next);