nixos-generate-config: preserve vfat filesystem mount permissions

The default is to mount these world-readable, but that's a security risk
for the EFI System Partition.

Ref https://github.com/NixOS/nixpkgs/issues/279362.

nixos/modules/installer/tools/nixos-generate-config.pl

···
         }
     }
 
+    # Preserve umask (fmask, dmask) settings for vfat filesystems.
+    # (The default is to mount these world-readable, but that's a security risk
+    # for the EFI System Partition.)
+    if ($fsType eq "vfat") {
+        for (@superOptions) {
+            if ($_ =~ /fmask|dmask/) {
+                push @extraOptions, $_;
+            }
+        }
+    }
+
     # is this a stratis fs?
     my $stableDevPath = findStableDevPath $device;
     my $stratisPool;