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_if.h

@@ -0,0 +1,102 @@
+/*
+ * PF-on-Linux: ifnet/address registry — OpenBSD `struct ifnet`/`in_ifaddr`
+ * views over Linux net_device + in_ifaddr lists (ISC 2026).
+ */
+#ifndef _PFK_IF_H
+#define _PFK_IF_H
+
+struct pfk_ifaddr {
+	struct pfk_ifaddr	*ifa_next;
+	struct pfk_ifnet	*ifa_ifp;
+	int			ifa_refcnt;
+	int			ifa_flags;	/* BSD IFA_* */
+	struct sockaddr_storage	ifa_addr_storage;	/* BSD-ish sockaddr */
+	struct sockaddr		*ifa_addr;	/* -> storage */
+	struct sockaddr		*ifa_mask;
+	struct net_device	*dev;
+	__be32			addr4;
+	struct in6_addr		addr6;
+	int			family;		/* AF_INET/AF_INET6 */
+	int			scope;		/* link/site for v6 */
+};
+
+struct pfk_ifqueue;	/* M5 */
+
+struct pfk_ifnet {
+	char			if_xname[IFNAMSIZ];
+	int			if_index;
+	struct net_device	*dev;
+	int			if_flags;	/* BSD-mapped IFF_* */
+	int			if_xflags;	/* BSD IFFX_* */
+	int			if_type;	/* IFT_* */
+	int			if_mtu;
+	void			*if_softc;
+	struct pfk_ifaddr	*if_addrlist;	/* refreshed snapshot */
+	struct pf_kif		*if_pf_kif;	/* pf_if glue */
+	struct pfk_ifqueue	*if_snd;	/* M5 */
+	void			*if_pf_rtable;	/* unused (rt tables NG) */
+	int			if_rdomain;	/* always 0 (NG), kept for ABI */
+	struct rcu_head		rcu;
+	struct list_head	link;
+	int			alive;
+};
+
+#define if_output		pfk_if_output_placeholder
+struct pfk_ifnet *pfk_ifp_byindex(int idx);		/* NULL if gone */
+struct pfk_ifnet *pfk_ifp_byname(const char *name);
+struct pfk_ifnet *pfk_ifp_bydev(struct net_device *dev);
+int	 pfk_if_addrlist_refresh(struct pfk_ifnet *ifp); /* NET_LOCK held */
+void	 pfk_if_free(struct pfk_ifnet *ifp);
+
+/* BSD IFF_* bits (OpenBSD values) — distinct from Linux! */
+#define PFIFF_UP		0x00000001
+#define PFIFF_BROADCAST		0x00000002
+#define PFIFF_DEBUG		0x00000004
+#define PFIFF_LOOPBACK		0x00000008
+#define PFIFF_POINTOPOINT	0x00000010
+#define PFIFF_RUNNING		0x00000040
+#define PFIFF_PROMISC		0x00000100
+#define PFIFF_ALLMULTI		0x00000200
+#define PFIFF_MULTICAST		0x00008000
+#define PFIFF_RESOLVE		0x02000000
+#define PFIFF_IPV4		0x10000000
+#define PFIFF_IPV6		0x20000000
+
+/* NOTE: BSD IFF_* bit values are PFIFF_*; staged port files are sed'ed
+ * IFF_* → PFIFF_* (IFF_ macros must NEVER alias linux netdev flags).
+ * BSD IFA_* */
+#define IFA_BROADCAST_	0x02
+#define IFA_PRIMARY_	0x04
+#define IFA_SECONDARY_	0x08
+
+struct mbuf_list { struct mbuf *ml_first, *ml_last; int ml_len; };
+
+/* egress interface (default-route dev), maintained on fib/net events */
+struct pfk_ifnet *pfk_egress_if(void);
+void pfk_egress_refresh(void);
+
+int  pfk_if_init(void);
+void pfk_if_exit(void);
+void pfk_if_refresh(struct pfk_ifnet *ifp);
+struct pfk_ifnet *pfk_if_first(void);
+struct pfk_ifnet *pfk_if_next(struct pfk_ifnet *ifp);
+struct pfk_ifnet *pfk_if_next_from(int *idp);
+struct net_device *ip_rt_get_default_dev(struct net *net);
+
+/* xmit API used by pf_route/pf output (implemented in pfk_xmit.c) */
+int if_output_tso(struct pfk_ifnet *ifp, struct mbuf **mp,
+	struct sockaddr *dst, void *rt, int mtu);
+int if_output_ml(struct pfk_ifnet *ifp, struct mbuf_list *ml,
+	struct sockaddr *dst, void *rt);
+int if_enqueue(struct pfk_ifnet *ifp, struct mbuf *m);
+
+/* addr lookups (ifa_ifwithaddr, in_ifwithaddr etc.) */
+struct pfk_ifaddr *pfk_ifwithaddr(const struct sockaddr *sa);
+struct pfk_ifaddr *pfk_ifwithroute(int family, const struct sockaddr *dst,
+	const struct sockaddr *gate, struct pfk_ifnet **ifp_out);
+
+/* mib-ish status for pfctl DIOCGIFSTATS */
+struct pfk_if_data { unsigned long long ifi_ibytes, ifi_obytes; };
+void pfk_if_stats(struct pfk_ifnet *ifp, struct pfk_if_data *out);
+
+#endif /* _PFK_IF_H */