nfp: use netif_set_real_num_queues()

Avoid reconfig problems due to failures in netif_set_real_num_tx_queues()
by using netif_set_real_num_queues().

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>