M1 progress: engine port compiles except pf.c; AF_DIVERT socket family; ifq framework

- compat layer extended through the full BSD API surface pf_ioctl/pf_lb/
  pf_if/pf_norm/pf_table/pf_ruleset/radix/md5/sha2 need (all compile):
  cpumem/counters model, ifaddr/ifg groups, cred view, endian+in6 names,
  NAT46/64, SipHash24, mbuf_list, frag6 helpers, ip6 forward/checksum,
  tcp options/FSM names, taskqueue & sysctl shims (documented in
  docs/porting-notes.md)
- pfsrc/divert_sock.c: real BSD divert(4) as runtime-registered PF_DIVERT=32
  socket family inside the module (sock_register; NPROTO=AF_MAX=45 -> zero
  core patches); divert_packet/divert6_packet wired for pf.c
- compat/pfk_ifq.c: OpenBSD 8.0 ifq framework with priq back end; hfsc and
  fq_codel aliases pending M5 (recorded in feature matrix as pending)
- design + plan updated for the divert decision (user-requested)
- stage-port.sh: single deterministic rename program for headers and .c

module/compat/pfk_xmit.c

@@ -206,3 +206,20 @@ pfk_send_icmp_error(int family, struct sk_buff *skb_in, int type, int code,
 /* NOTE: TCP RST generation is done by PF itself (pf.c builds the segment
  * and calls if_output_tso), so no kernel tcp_v4_send_reset export is
  * needed — matches OpenBSD's pf_send_rst() design. */
+
+/*
+ * pfk_if_output(ifp, m, dst, rt): BSD if_output() equivalent used by the
+ * ported PF code (route-to / refragment / divert paths).
+ */
+int
+pfk_if_output(struct pfk_ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
+    void *rt)
+{
+	struct mbuf *mp = m;
+	int err;
+
+	err = if_output_tso(ifp, &mp, dst, rt, ifp->if_mtu);
+	if (mp)
+		m_freem(mp);
+	return err;
+}