linux-4.13: mark as insecure (+required generic changes)

extraMeta was being fed as passthru without being processed by stdenv,
so without those changes, adding the security attribute would be useless.

pkgs/os-specific/linux/kernel/generic.nix

@@ -118,7 +118,7 @@ let
   };
 
   kernel = buildLinux {
-    inherit version modDirVersion src kernelPatches stdenv;
+    inherit version modDirVersion src kernelPatches stdenv extraMeta;
 
     configfile = configfile.nativeDrv or configfile;
 
@@ -131,10 +131,7 @@ let
 
   passthru = {
     features = kernelFeatures;
-
-    meta = kernel.meta // extraMeta;
-
-    passthru = kernel.passthru // (removeAttrs passthru [ "passthru" "meta" ]);
+    passthru = kernel.passthru // (removeAttrs passthru [ "passthru" ]);
   };
 
   nativeDrv = lib.addPassthru kernel.nativeDrv passthru;