i40e: count timeout events

The ethtool -S statistics should have a counter for
tx timeouts in order to better help inform the masses.

Change-ID: Ice4b20ed4a151509f366719ab105be49c9e7b2b4
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>