bandwidthd - rotate log files when output_cdf is enabled

The log files should be rotated each night when output_cdf is on. The cron job sends the "HP" to bandwidthd. The bandwidthd program already implements the log rotation scheme when it receives the HUP signal. Documentation added to the UI so people can learn/understand what happens.
No need to update the package version for now - I need to also make a change to allow regular saving of log data on nanoBSD, so I will update the package version when that change comes.