Implement DoS protection

[AlyaGomaa]

1. Count flows per min during the input

min_threshold is 2000 flows per min.

2. If the count is below the min_threshold, work normally
3. If the count is above the min_threshold, do sampling like this
4. Sample with ratio sr for 1 min duration. (The sample ratio depends on the flows/min value)
   Flows/min is fm
   sample ratio(fm) = (X^2)/20000
   If X = 2000, sr = 200
   If X = 3000, sr = 450
   If X = 4000, sr = 800
5. After 1 minute sampling, we go back to process all flows to count the flows/min again
6. Count how many flows/min (only 6 sec, and multiply by 10)
7. do again the check