help: Restart DNS forwarding

run:
      if cli-shell-api existsActive service dns forwarding; then
          echo "Restarting DNS forwarding..."
          sudo /opt/vyatta/sbin/vyatta-dns-forwarding.pl --restart-dnsforwarding;
          if [[ $? -eq 0 ]]; then
              echo "Success!"
          fi
      else
          echo "DNS forwarding is not configured"
      fi