i40e: fix link checking logic

If the interface is closed, but VFs exist, current code will spam all
the VFs with link messages every second. This is because the link event
code was looking at netif_carrier_ok() without checking to see if the
interface was actually open.

Refactor the logic to only check the carrier state if the interface is
actually open. This allows link changes to be reported correctly without
spamming the VFs.

Change-ID: If136e79bb3820d21ea4e39e332e8a9604efc2b2a
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Patrick Lu <patrick.lu@intel.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>