Fix issue #17996: expose socket.AF_LINK constant on BSD and OSX.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 20db3d9..fa75a10 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -5658,6 +5658,9 @@
     /* Alias to emulate 4.4BSD */
     PyModule_AddIntMacro(m, AF_ROUTE);
 #endif
+#ifdef AF_LINK
+    PyModule_AddIntMacro(m, AF_LINK);
+#endif
 #ifdef AF_ASH
     /* Ash */
     PyModule_AddIntMacro(m, AF_ASH);