net/mlx5: fix HW counters path in switchdev mode

net/mlx5: fix HW counters path in switchdev mode

When debugging performance of a DPDK application the user may
need to view the different statistics of DPDK (for example out_of_buffer)
This can be enabled by using testpmd command 'show port xstats
<port_id>' for example.

The current implementation assumes legacy mode in which the counters
are at <ibdev_path>/<port_id>/hw_counters/<file_name>.
In switchdev mode the counters file is located right after the device
name, hence resides at <ibdev_path>/hw_counters.

The fix tries to open the path in the second location after a failure
to open the file from the first location.

Fixes: 9c0a9eed37f1 ("net/mlx5: switch to the names in the shared IB context")
Cc: stable@dpdk.org
Signed-off-by: Shy Shyman <shys@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>