M1: compat layer + pf.ko skeleton builds against Linux 7.3.4

- pfk.h: BSD types/ioctl encoding (OpenBSD bit layout), locks (NET_LOCK=rwsem),
  pools, timeouts, mbuf shim over sk_buff, ifnet registry, toeplitz/siphash
- pfk_mod/pfk_hooks: misc /dev/pf (0600), IPv4 netfilter hook skeleton,
  DIOCGETSTATUS answered (M1 skeleton; engine ioctls land with pf_ioctl.c)
- vendorize/stage-port scripts: deterministic upstream staging with seds
  (struct renames, IFF_*->PFIFF_*, sa_len drops) logged to docs/porting-notes
- fixes: modules_prepare+Module.symvers for out-of-tree builds

module/include/pfk_api.h

@@ -0,0 +1,13 @@
+/* PFLINUX internal API (module-internal prototypes) */
+#ifndef _PFK_API_H
+#define _PFK_API_H
+#include <pfk.h>
+#include <net/pfvar.h>
+
+long pfk_ioctl(struct file *f, unsigned int cmd, unsigned long addr);
+int  pfk_enable(int on);
+void pfk_status(struct pf_status *s);
+int  pfk_hooks_register(void);
+void pfk_hooks_unregister(void);
+
+#endif