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/compat/sys/endian.h

@@ -0,0 +1,6 @@
+/* PFLINUX compat: <sys/endian.h> */
+#ifndef _PFK_SYS_ENDIAN_H
+#define _PFK_SYS_ENDIAN_H
+#include <linux/byteorder/generic.h>
+#include <linux/byteorder/little_endian.h>
+#endif