i40e/i40evf: adjust interrupt throttle less frequently

i40e/i40evf: adjust interrupt throttle less frequently

Orabug: 22342532

The adaptive ITR (interrupt throttle rate) algorithm was adjusting
the hardware's interrupt rate too frequently.  This caused a lot
of variation in the interrupt rate for fairly constant workloads.

Change the code to have a counter and adjust only once every N
number of interrupts.

Change-ID: I0460f1f86571037484eca5aca36ac4d889cb8389
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit ee2319cf17ee64bbd0096f2f8f3f8390c93b1e39)
Signed-off-by: Brian Maly <brian.maly@oracle.com>