vlan: updates vlan real_num_tx_queues

Updates real_num_tx_queues in case underlying real device
has changed real_num_tx_queues.

-v2
 As per Eric Dumazet<eric.dumazet@gmail.com> comment:-
   -- adds BUG_ON to catch case of real_num_tx_queues exceeding num_tx_queues.
   -- created this self contained patch to just update real_num_tx_queues.

Signed-off-by: Vasu Dev <vasu.dev@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>