i40e: trigger SW INT with no ITR wait

Since we want the SW INT to go off as soon as possible, write the
extra bits that will turn off the ITR wait for the interrupt.

Change-ID: I6d5382ba60840fa32abb7dea17c839eb4b5f68f7
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>