net/mlx5: fix xstats reset reinitialization

net/mlx5: fix xstats reset reinitialization

The mlx5_xstats_reset clears the device extended statistics.
In this function the driver may reinitialize the structures
that are used to read device counters.

In case of reinitialization, the number of counters may
change, which wouldn't be taken into account by the
reset API callback and can cause a segmentation fault.

This issue is fixed by allocating the counters size after
the reinitialization.

Fixes: a4193ae3bc4f ("net/mlx5: support extended statistics")
Cc: stable@dpdk.org
Reported-by: Ralf Hoffmann <ralf.hoffmann@allegro-packets.com>
Signed-off-by: Shiri Kuzin <shirik@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>