i40e: fix lookup table when RSS disabled/enabled

This patch fixes the bug which causes RSS to continue to work
after being disabled.  After disabling RSS, traffic would continue
to be assigned to different queues instead of falling back to a
single queue. Without this patch, attempting to disable RSS would
not work as expected. This patch fixes the bug by clearing the
lookup table used by RSS such that all traffic is assigned to a
single queue.  This patch also addresses the issue of reinstating
 the lookup table should RSS then be re-enabled.

Change-ID: Ib20c7c6a7e9f1f772bb787370f8a8c664796b141
Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>