i40e: rtnl_lock in reset path fixes

Any user-initiated path which eventually calls reset needs
to hold the rtnl_lock, so add functionality to do that.

Be careful not to use the safe reset when cleaning up
from the diagnostic tests, which avoids rtnl_lock
recursion from ethtool.

Protect the reset_task with rtnl_lock, since it runs from a work item.

Change-Id: Ib6e7a3fb2966809db2daf35fd5a123ccdf6f6f0f
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>