ixgbevf: setup queue counts

Add calls for netif_set_real_num_t/rx_queues() in ixgbevf_open().
Make sure that calls to ixgbevf_open() are rtnl protected and improve
the error handling when setting up multiple queues.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>