[netstat]: Fix for negative output values of counters after clear cou…

…nters operation (#697)

Immediately after a clear counter operation, the difference between new
counter and old counter is negative. Returning 0 in this situation

utilities_common/netstat.py

@@ -13,7 +13,7 @@ def ns_diff(newstr, oldstr):
  return STATUS_NA
  else:
  new, old = int(newstr), int(oldstr)
- return '{:,}'.format(new - old)
+ return '{:,}'.format(max(0, new - old))
 
 def ns_brate(newstr, oldstr, delta):
  """