ixgbe: update real_num_tx_queues on changing num_rx_queues

Move the update of real_num_tx_queues from
ixgbe_acquire_msix_vectors() to ixgbe_set_num_queues(), to ensure it
be always in sync with num_tx_queues.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>