unbound service: non-blocking random in chroot

/dev/random is an exhaustible resource. Presumably, unbound will not be
used to generate long-term encryption keys and so allowing it to use
/dev/random only increases the risk of entropy exhaustion for no
benefit.

nixos/modules/services/networking/unbound.nix

@@ -115,7 +115,7 @@ in
         chown unbound ${stateDir} ${rootTrustAnchorFile}
         ''}
         touch ${stateDir}/dev/random
-        ${pkgs.utillinux}/bin/mount --bind -n /dev/random ${stateDir}/dev/random
+        ${pkgs.utillinux}/bin/mount --bind -n /dev/urandom ${stateDir}/dev/random
       '';
 
       serviceConfig = {