all modules: wrap Linux-only code in #ifdef __linux__ — full macOS build works

Every kernel-LPE module that uses Linux-only headers (splice, posix_fadvise,
linux/netlink.h, sys/ptrace.h, etc.) now follows the same #ifdef __linux__
pattern the new modules already used: Linux body in the ifdef, stub
detect/exploit/cleanup returning SKELETONKEY_PRECOND_FAIL on non-Linux,
platform-neutral rule strings + module struct + register fn left outside.

14 modules wrapped:
  dirty_pipe (already done above), af_packet, af_packet2,
  cgroup_release_agent, cls_route4, dirty_cow, fuse_legacy,
  netfilter_xtcompat, nf_tables, nft_fwd_dup, nft_payload,
  overlayfs, overlayfs_setuid, ptrace_traceme.

Several modules previously had ad-hoc partial stubs (af_packet2 faked
SIOCSIFFLAGS/MAP_LOCKED, netfilter_xtcompat faked sysv-msg syscalls,
the nft_* modules had 3 partial __linux__ islands each, fuse_legacy /
nf_tables had inner-only ifdef blocks) — all replaced with the uniform
outer-wrap shape from dirty_pipe / dirtydecrypt / fragnesia / pack2theroot.

Where a module includes core/kernel_range.h, core/finisher.h, or
core/offsets.h, those are now inside the ifdef block as well — silences
clangd's "unused-includes" LSP warning on macOS while keeping them
present for the real Linux build.

No exploit logic, constant, struct, shellcode byte, or rule string was
modified — only include placement and ifdef markers.

Build verification:
  macOS (local): make clean && make → Mach-O x86_64, 31 modules
                 registered, --scan reports each Linux-only module as
                 "Linux-only module — not applicable here".
  Linux (docker gcc:latest + libglib2.0-dev): make clean && make →
                 ELF 64-bit, 31 modules. Exploit code paths unchanged.

modules/af_packet_cve_2017_7308/skeletonkey_modules.c

@@ -60,17 +60,22 @@
 
 #include "skeletonkey_modules.h"
 #include "../../core/registry.h"
-#include "../../core/kernel_range.h"
-#include "../../core/offsets.h"
-#include "../../core/finisher.h"
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <string.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+#ifdef __linux__
+
+#include "../../core/kernel_range.h"
+#include "../../core/offsets.h"
+#include "../../core/finisher.h"
+
 #include <errno.h>
 #include <fcntl.h>
-#include <unistd.h>
 #include <sched.h>
 #include <sys/wait.h>
 #include <sys/socket.h>
@@ -858,6 +863,30 @@ static skeletonkey_result_t af_packet_exploit(const struct skeletonkey_ctx *ctx)
 #endif
 }
 
+#else  /* !__linux__ */
+
+/* Non-Linux dev builds: AF_PACKET + unshare(CLONE_NEWUSER|CLONE_NEWNET)
+ * + TPACKET_V3 ring are Linux-only kernel surface; the TPACKET_V3
+ * integer-overflow primitive is structurally unreachable elsewhere.
+ * Stub out cleanly so the module still registers and `--list` /
+ * `--detect-rules` work on macOS/BSD dev boxes — and so the top-level
+ * `make` actually completes there. */
+static skeletonkey_result_t af_packet_detect(const struct skeletonkey_ctx *ctx)
+{
+    if (!ctx->json)
+        fprintf(stderr, "[i] af_packet: Linux-only module "
+                "(AF_PACKET TPACKET_V3 + user_ns) — not applicable here\n");
+    return SKELETONKEY_PRECOND_FAIL;
+}
+static skeletonkey_result_t af_packet_exploit(const struct skeletonkey_ctx *ctx)
+{
+    (void)ctx;
+    fprintf(stderr, "[-] af_packet: Linux-only module — cannot run here\n");
+    return SKELETONKEY_PRECOND_FAIL;
+}
+
+#endif /* __linux__ */
+
 static const char af_packet_auditd[] =
     "# AF_PACKET TPACKET_V3 LPE (CVE-2017-7308) — auditd detection rules\n"
     "# Flag AF_PACKET socket creation from non-root via userns.\n"