i40e: refactor ethtool tests

Put the print and reset statements in the actual test functions to make
them more self-contained, and only run the reset for tests that need it.

Change-Id: Ic70f49b11bf8bae82e59d8fd25b46215c90c4510
Signed-off-by: Shannon Nelson <shannon.nelson@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>