net/mlx5: fix RSS RETA reset on start

net/mlx5: fix RSS RETA reset on start

The following sequences was working fine on mlx5:
   rte_eth_dev_configure(portid, ...);

   for (queueid = 0; queueid < nb_txq; queueid++)
      rte_eth_tx_queue_setup(portid, queueid, ...);

   for (queueid = 0; queueid < nb_rxq; queueid++)
      rte_eth_rx_queue_setup(portid, queueid, ...);

  // use a custom reta configuration
  rte_eth_dev_rss_reta_update(portid, reta_conf, reta_size);
  rte_eth_dev_start(portid);

We were able to configure a custom reta before starting the port.

The commit "net/mlx5: support RSS on hairpin" breaks this logic by
moving the code initializing the RSS reta from rte_eth_dev_configure
into rte_eth_dev_start.

To fix the issue, the skip_default_rss_reta is always set to 1 in
rte_eth_dev_rss_reta to avoid reconfigure the rss reta when the device
is started.

Fixes: 63bd16292c3a ("net/mlx5: support RSS on hairpin")
Cc: stable@dpdk.org
Signed-off-by: Maxime Leroy <maxime.leroy@6wind.com>
Acked-by: Ori Kam <orika@nvidia.com>