i40e: Fix a bug where Rx would stop after some time

Move the setting of flow control because this should be done at a pf level not
a vsi level. Also add a sleep and restart an to fix a bug where Rx would stop
after some stress.

Change-ID: I9a93d8c2ff27c39339eb00bc4ec1225e43900be0
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>