qemu: switch to building wireless as kernel modules

This is a hefty change

* add support for kernel backports project
* build wireless stack/drivers as modules from a backported kernel
* create a service to load/unload the modules

pkgs/kernel-backport/default.nix

@@ -0,0 +1,80 @@
+{ stdenv
+, git
+, python2
+, which
+, fetchgit
+, fetchpatch
+, fetchFromGitHub
+, autoreconfHook
+, coccinelle
+}:
+let
+  donorTree = fetchFromGitHub {
+    owner = "torvalds";
+    repo = "linux";
+    rev = 	"e2c1a934fd8e4288e7a32f4088ceaccf469eb74c"; # 5.15.94
+    hash= "sha256-Jg3EgL86CseuzYMAlUG3CDWPCo8glMSIZs10l7EuhWI=";
+  };
+  backports = stdenv.mkDerivation {
+    name = "linux-backports";
+    version = "dfe0f60ca8a";
+    nativeBuildInputs = [ python2 ];
+
+    src = fetchgit {
+      url = "https://git.kernel.org/pub/scm/linux/kernel/git/backports/backports.git";
+      name = "backports";
+      rev = "dfe0f60ca8a1065e63b4db703b3bd2708ee23a0e";
+      hash = "sha256-V+unO0rCom+TZS7WuaXFrb3C1EBImmflCPuOoP+LvBY=";
+    };
+    buildPhase = ''
+      patchShebangs .
+    '';
+    installPhase = ''
+      mkdir -p $out
+      cp -a . $out
+      rm $out/patches/0073-netdevice-mtu-range.cocci
+      # fq.patch is obsoleted by kernel commit 48a54f6bc45 and no longer
+      # applies
+      # rm $out/patches/0091-fq-no-siphash_key_t/fq.patch
+      # don't know why this doesn't apply but it's only important for
+      # compiling against linux < 4.1
+      # rm $out/patches/0058-ptp_getsettime64/ptp_getsettime64.cocci
+    '';
+    patches = [
+      # (fetchpatch {
+      #   url = "https://github.com/telent/nixwrt/blob/28ff2559e811c740b0a2922f52291b335804857b/nixwrt/kernel/gentree-writable-outputs.patch";
+      #   hash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
+      # })#
+      ./gentree-writable-outputs.patch
+#      ./update-usb-sg-backport-patch.patch
+#      ./backport_kfree_sensitive.patch
+    ];
+  };
+in stdenv.mkDerivation rec {
+  inherit donorTree;
+  KERNEL_VERSION = builtins.substring 0 11 donorTree.rev;
+  BACKPORTS_VERSION = backports.version;
+  name = "backported-kernel-${KERNEL_VERSION}-${BACKPORTS_VERSION}";
+
+  # gentree uses "which" at runtime to test for the presence of git,
+  # and I don't have the patience to patch it out. There is no other
+  # reason we need either of them as build inputs.
+  depsBuildBuild = [ coccinelle ];
+  nativeBuildInputs = [ which git python2 ];
+
+  phases = [
+    "backportFromFuture" "installPhase"
+  ];
+
+  backportFromFuture = ''
+    echo $KERNEL_VERSION $BACKPORTS_VERSION
+    WORK=`pwd`/build
+    mkdir -p $WORK
+    cat ${backports}/copy-list > copy-list
+    echo 'include/linux/key.h' >> copy-list
+    python  ${backports}/gentree.py --verbose --clean  --copy-list copy-list ${donorTree} $WORK
+  '';
+  installPhase = ''
+    cp -a ./build/ $out
+  '';
+}