igb: make sure SR-IOV init uses the right number of queues

Recent changes to igb_probe_vfs() could lead to the PF holding onto all
of the queues. Reorder igb_probe_vfs() to be before
gb_init_queue_configuration() and add some more error checking.

Signed-off-by: Todd Fujinaka <todd.fujinaka@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>