net/mlx5: fix completion buffer size

net/mlx5: fix completion buffer size

Completion buffer size was computed wrongly, causing
completion polling to wraparound too early and miss entries.

Fixing it by using Direct Verbs to query the CQ info.

Fixes: 6218063b39a6 ("net/mlx5: refactor Rx data path")
Fixes: 1d88ba171942 ("net/mlx5: refactor Tx data path")
Cc: stable@dpdk.org
Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>