nixos/malloc: set vm.max_map_count when using graphene-hardened

nixos/modules/config/malloc.nix

@@ -97,6 +97,7 @@ in
   };
 
   config = mkIf (cfg.provider != "libc") {
+    boot.kernel.sysctl."vm.max_map_count" = mkIf (cfg.provider == "graphene-hardened") (mkDefault 1048576);
     environment.etc."ld-nix.so.preload".text = ''
       ${providerLibPath}
     '';