Graph number of associated clients

[mglb1]

For any interface that is operating as an AP (ie, iwconfig reports the interface is in master mode) we should be able to graph the number of currently associated clients. For madwifi interfaces this can be found by looking at the /proc/net/madwifi/<ifname>/associated_sta file.

The CRCNET-MIB should be extended to contain an OID for this value, crcnet-monitor should be extended to populate it for all AP interfaces and whatever other infrastructure in the configuration system that is needed to make these graphs start to magically appear in the interface should be updated too.

[mglb1]

Implemeted in r1370