nixos-generate-config: Configure networking.hostId by default

The host id value gets generated by reading a 32-bit value from
/dev/urandom.

This makes programs that rely on a correct host id more reliable.

It also makes using ZFS more seamless, as you don't need to configure
the hostId manually; instead, it becomes part of your config from the
moment you install NixOS.

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

@@ -476,6 +476,14 @@ EOF
 EOF
         }
 
+        # Generate a random 32-bit value to use as the host id
+        open my $rnd, "<", "/dev/urandom" or die $!;
+        read $rnd, $hostIdBin, 4;
+        close $rnd;
+
+        # Convert the 32-bit value to a hex string
+        my $hostIdHex = unpack("H*", $hostIdBin);
+
         write_file($fn, <<EOF);
 # Edit this configuration file to define what should be installed on
 # your system.  Help is available in the configuration.nix(5) man page
@@ -491,6 +499,7 @@ EOF
 
 $bootLoaderConfig
   # networking.hostName = "nixos"; # Define your hostname.
+  networking.hostId = "$hostIdHex";
   # networking.wireless.enable = true;  # Enables wireless.
 
   # Select internationalisation properties.