linux: forward features into passthru

build.nix accepted `features` as a parameter but discarded it, never
placing it into the derivation's passthru. The NixOS boot.kernelPackages
apply function calls kernel.override() on every evaluation, re-running
build.nix from scratch; any features added via overrideAttrs were
silently lost, causing assertions like hardware.graphics.enable32Bit
(which checks kernel.features.ia32Emulation) to always fail for
linuxManualConfig-based kernels.

Change `features ? null` to `features ? {}` and add it to passthru so
it survives override() call chains.

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

@@ -80,8 +80,7 @@ lib.makeOverridable (
 
     # Whether to utilize the controversial import-from-derivation feature to parse the config
     allowImportFromDerivation ? false,
-    # ignored
-    features ? null,
+    features ? { },
     lib ? lib_,
     stdenv ? stdenv_,
   }:
@@ -530,6 +529,9 @@ lib.makeOverridable (
       inherit
         isZen
         withRust
+        # Forwarded into passthru so features survive kernel.override() call chains
+        # used by the NixOS module system (see boot.kernelPackages apply in kernel.nix).
+        features
         ;
       baseVersion = lib.head (lib.splitString "-rc" version);
       kernelOlder = lib.versionOlder baseVersion;