pkgs/rtw89: Add src override at unstable-2021-10-21

That version includes IPv6 support.

pkgs/default.nix

@@ -86,4 +86,26 @@ in
       ]);
     });
   };
+} // (
+  let
+    rtw89AttrsOverride = (o: o // {
+      version = "unstable-2021-10-21";
+
+      src = prev.fetchFromGitHub {
+        owner = "lwfinger";
+        repo = "rtw89";
+        rev = "0684157cba90e36bff5bc61a59e7e87c359b5e5c";
+        sha256 = "sha256-YhiusEMwchY9XazwE1auFqJ1qL6R/4vy7InrGaLnajM=";
+      };
+    });
+  in
+  {
+    linuxPackages = prev.linuxPackages.extend (lpfinal: lpprev: {
+      rtw89 = lpprev.rtw89.overrideAttrs rtw89AttrsOverride;
+    });
+
+    linuxPackages_latest = prev.linuxPackages_latest.extend (lpfinal: lpprev: {
+      rtw89 = lpprev.rtw89.overrideAttrs rtw89AttrsOverride;
+    });
   }
+)