net/mlx5: fix hairpin flow split decision

net/mlx5: fix hairpin flow split decision

Previously, the identification of hairpin queue was done using
mlx5_rxq_get_type() function.
Recent patch replaced it with use of mlx5_rxq_get_hairpin_conf(),
and check of the return value conf != NULL.
The case of return value is NULL (queue is not hairpin) was not handled.
As result, non-hairpin flows were wrongly handled.
This patch adds the required check for return value is NULL.

Fixes: 509f8470de55 ("net/mlx5: do not split hairpin flow in explicit mode")
Cc: stable@dpdk.org
Signed-off-by: Dekel Peled <dekelp@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>