Add a stub for kernel_ll_addresses on Mac OS X.

It still won't work, but will at least compile.
Reported by Mathias Mahnke.

kernel_socket.c

@@ -616,6 +616,14 @@ kernel_addresses(char *ifname, int ifindex,
     return -1;
 }
 
+int
+kernel_ll_addresses(char *ifname, int ifindex,
+                    struct kernel_route *routes, int maxroutes)
+{
+    errno = ENOSYS;
+    return -1;
+}
+
 int
 kernel_callback(int (*fn)(int, void*), void *closure)
 {