ibmvnic: Revise RX/TX queue error messages

During a device failover, there may be latency between the loss
of the current backing device and a notification from firmware that
a failover has occurred. This latency can result in a large amount of
error printouts as firmware returns outgoing traffic with a generic
error code. These are not necessarily errors in this case as the
firmware is busy swapping in a new backing adapter and is not ready
to send packets yet. This patch reclassifies those error codes as
warnings with an explanation that a failover may be pending. All
other return codes will be considered errors.

Signed-off-by: Thomas Falcon <tlfalcon@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>