i40e: fix for queue timing delays

This patch adds a delay to Rx queue disables to accommodate HW needs.

v2: Added missing check for disable only, additional details on the
need for the ugly delay and fixed spacing on comment.

Change-ID: I2864ca667ce5dcc2cc44f8718113b719742a46a1
Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>