Revert "linux*: remove 3.14, as it's no longer maintained"

This is the simplest way to reenable the use of BLCR
(which at present requires linux version >3.12 <3.18)
until we find a better solution.

This reverts commit 6a9e765e27.

pkgs/os-specific/linux/kernel/linux-3.14.nix

@@ -0,0 +1,19 @@
+{ stdenv, fetchurl, perl, buildLinux, ... } @ args:
+
+import ./generic.nix (args // rec {
+  version = "3.14.77";
+  extraMeta.branch = "3.14";
+
+  src = fetchurl {
+    url = "mirror://kernel/linux/kernel/v3.x/linux-${version}.tar.xz";
+    sha256 = "1v3cc3ddla2b8gkwbms4x3lbjygw87r13150nikf1gc0hf64rqp0";
+  };
+
+  kernelPatches = args.kernelPatches;
+
+  features.iwlwifi = true;
+  features.efiBootStub = true;
+  features.needsCifsUtils = true;
+  features.canDisableNetfilterConntrackHelpers = true;
+  features.netfilterRPFilter = true;
+} // (args.argsOverride or {}))