RADIUS hook tweaks for Cisco hardware: optional different formatting of a parameter

There's a support#16875, asking for solution to the RADIUS problem with non-standard formatting for a parameter. In this deployment, a Cisco hardware is used as RADIUS server.

The implementation expects the radius attribute conveying the MAC address to use a non-standard 0000.0000.0000, rather than the typical 00:00:00:00:00:00.

I haven't looked at the implementation, but it seems reasonable to provide an optional formatting knob that, when enabled, will use this alternative formatting. The default should remain as it is now.