ibmvnic: Do not disable device during failover or partition migration

During a device failover or partition migration reset, it is not
necessary to disable the backing adapter since it should not be
running yet and its Command-Response Queue is closed. Sending
device commands during this time could result in an error or
timeout disrupting the reset process. In these cases, just halt
transmissions, clean up resources, and continue with reset.

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