PfSense 2.3.4 absolute value problem in monitoring graphs (NTP)

[bfeitell]

The monitoring graphs for NTP are very wrong.  The maxima and mimima for the offset are being calculated as signed numbers, rather than as absolute values relative to zero.

Please see the attached image showing NTP for an 8 hour span at 1 minute resolution.  The hover box shows an offset of -0.01 ms, which should be presented as the minimum offset in the chart below.  Instead the chart shows a minimum of -0.54 ms, which is the signed number minimum offset, but the absolute value maximum.  Likewise the maximum is shown as 0.30 ms, which I expect is the signed maximum offset over the time period, but is not the correct absolute value maximum, which is |-0.54| ms.


[phil.davis]

I think both the plus/minus offset graph and stats and the absolute offset graph and stats are useful.
The plus/minus offset average gives you an idea if the offset drifts around but averages close to zero.
The absolute offset gives you an idea of how much off it is, regardless of plus/minus.

So I added the absolute offset stat to the display.

Redmine https://redmine.pfsense.org/issues/7548

PR https://github.com/pfsense/FreeBSD-ports/pull/354