This patch fixes possible division by zero in receive
interrupt handler when working without adaptive interrupt
moderation.

The adaptive interrupt moderation mechanism is typically
disabled on jumbo MTUs.
Signed-off-by: NDmitry Fleytman <dmitry@daynix.com>
Signed-off-by: NLeonid Bloch <leonid@daynix.com>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>