i40e: support VF link state ndo

This netdev op allows the PF driver to control the virtual link state of
the VF devices. This can be used to deny naughty VF drivers access to
the wire, or to allow VFs (regardless of temperament) to communicate
with each other over the device's internal switch even though external
link is down.

Add the actual ndo function, and modify vc_notify_link_state to check
the link status of each VF before sending a message in the case when
physical link changes state.

Change-ID: Ib5a6924da78c540789f21d26b5e8086d71c29384
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>