[ Upstream commit 7c9864bb ]

If the accelerated networking SRIOV VF device has lost carrier
use the synthetic network device which is available as backup
path. This is a rare case since if VF link goes down, normally
the VMBus device will also loose external connectivity as well.
But if the communication is between two VM's on the same host
the VMBus device will still work.
Reported-by: "Shah, Ashish N" <ashish.n.shah@intel.com>
Fixes: 0c195567 ("netvsc: transparent VF management")
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>