Fix division by zero

[fm94]

This might solve issue #18

Background:
The flow length can be in the range of nano/micro-seconds, if it is converted to milliseconds then the uint operation floors it into a 0 which means computing a rate (pkts/time) yields an error. To solve this, the minimum allowed duration for a flow is 1 (unit).

The typical behavior is to return a +inf but since this doesn't make sense in networking I believe that dividing by 1 is better.

[notti]

Please don't modify generated files - but the generator (also look at the file header :) )
Also would look more sensible to me if we either set no value or nil in this case

[fm94]

So maybe we remove divide from gen_math.go because it requires special handling?

I've tested returning Inf or nil but that means dropping a lot of flows just because the flow duration, for instance, is bellow 1 millisec. I'm not sure how to handle this, maybe we should avoid casting into int.

[notti]

That is the wrong place then -> the place where you did the modification is just general division - so you wouldmodifiy division for everybody and everyone to do something to fake a 1 for 0 (for every integer case).
The time conversion happened already at the point where you tried to modified that.
Would be better to fix the number to what you want before - e.g. with an additional computation.

[fm94]

Closing this pull request and creating a new one with a different solution.