ixgbe: Update adaptive ITR algorithm

The following change is meant to update the adaptive ITR algorithm to
better support the needs of the network. Specifically with this change what
I have done is make it so that our ITR algorithm will try to prevent either
starving a socket buffer for memory in the case of Tx, or overrunning an Rx
socket buffer on receive.

In addition a side effect of the calculations used is that we should
function better with new features such as XDP which can handle small
packets at high rates without needing to lock us into NAPI polling mode.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>