ibmvnic: Fix pending MAC address changes

Due to architecture limitations, the IBM VNIC client driver is unable
to perform MAC address changes unless the device has "logged in" to
its backing device. Currently, pending MAC changes are handled before
login, resulting in an error and failure to change the MAC address.
Moving that chunk to the end of the ibmvnic_login function, when we are
sure that it was successful, fixes that.

The MAC address can be changed when the device is up or down, so
only check if the device is in a "PROBED" state before setting the
MAC address.

Fixes: c26eba03 ("ibmvnic: Update reset infrastructure to support tunable parameters")
Signed-off-by: Thomas Falcon <tlfalcon@linux.vnet.ibm.com>
Reviewed-by: John Allen <jallen@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>