Traffic accounting using netfilter through iptables

Accounting rules per IP in the lan address range are set up automatically each time this script is started.
The script is tailored towards OpenWRT.
The code is very simple at the cost of a few shortcomings:
- accounting is done on an IP address base instead of on a MAC address base
- very many addresses may be monitored
- resetting of the counters must be done manually
- inspection must be done through iptables
The first shortcoming can in general be alleviated by extending the dhcp lease time.
The second shortcoming can be alleviated by specifying a stringent netmask.