net/mlx5: fix Direct Verbs flow descriptor allocation

net/mlx5: fix Direct Verbs flow descriptor allocation

Initialize flow descriptor tunnel member during flow creation.
Prevent access to stale data and pointers when flow descriptor is
reallocated after release.
Fix flow index validation.

Fixes: e7bfa3596a0a ("net/mlx5: separate the flow handle resource")
Fixes: 8bb81f2649b1 ("net/mlx5: use thread specific flow workspace")
Cc: stable@dpdk.org
Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>