i40e: fix WoL support check

The current check for WoL on i40e is broken. Code comment says only
magic packet is supported, so only check for that.

Fixes: 540a152d

 (i40e/ixgbe/igb: fail on new WoL flag setting WAKE_MAGICSECURE)

Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>