ibmvnic: Fix passive VNIC server login process

In some cases, if there is no VNIC server available during the driver
probe, the driver should wait until it receives an initialization
request from the VNIC Server to start the login process. Recent testing
has show that this is incorrectly handled in the current driver.

The proposed solution handles this initialization request by scheduling
a task in the shared workqueue that completes the login process and
registers the net device.

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