linuxPackages.r8168: update broken

pkgs/os-specific/linux/r8168/default.nix

···
     license = licenses.gpl2Plus;
     platforms = platforms.linux;
     maintainers = with maintainers; [ timokau ];
-    broken = kernel.kernelAtLeast "5.17";
+    broken = (lib.versions.majorMinor kernel.modDirVersion) != "5.15";
   };
 }