ixgbe: move set_num_queues and call it after msix failure

This is partial preparation for a future patch which will extend
ixgbe_set_num_queues

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>