i40e: Cleanup Doxygen warnings

These changes make Doxygen/kdoc work correctly without warnings.

Change-ID: I2941f38860be805ff7548d84dae35754c83f1d62
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>