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/include/net/pfvar_priv.h

@@ -559,13 +559,13 @@ struct pf_pdesc {
 	u_int8_t	 destchg;	/* flag set when destination changed */
 	u_int8_t	 pflog;		/* flags for packet logging */
 	union {
-		struct tcphdr			tcp;
-		struct udphdr			udp;
-		struct icmp			icmp;
+		struct pf_tcphdr			tcp;
+		struct pf_udphdr			udp;
+		struct pf_icmp			icmp;
 #ifdef INET6
-		struct icmp6_hdr		icmp6;
-		struct mld_hdr			mld;
-		struct nd_neighbor_solicit	nd_ns;
+		struct pf_icmp6		icmp6;
+		struct pf_mld_hdr			mld;
+		struct pf_nd_neighbor_solicit	nd_ns;
 #endif /* INET6 */
 	} hdr;
 };