ibmvnic: Activate disabled RX buffer pools on reset

RX buffer pools are disabled while awaiting a device
reset if firmware indicates that the resource is closed.

This patch fixes a bug where pools were not being
subsequently enabled after the device reset, causing
the device to become inoperable.

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