net/mlx5: Bridge, ensure dev_name is null-terminated

commit 350d9a82 upstream.

Even though net_device->name is guaranteed to be null-terminated string of
size<=IFNAMSIZ, the test robot complains that return value of netdev_name()
can be larger:

In file included from include/trace/define_trace.h:102,
                    from drivers/net/ethernet/mellanox/mlx5/core/esw/diag/bridge_tracepoint.h:113,
                    from drivers/net/ethernet/mellanox/mlx5/core/esw/bridge.c:12:
   drivers/net/ethernet/mellanox/mlx5/core/esw/diag/bridge_tracepoint.h: In function 'trace_event_raw_event_mlx5_esw_bridge_fdb_template':
>> drivers/net/ethernet/mellanox/mlx5/core/esw/diag/bridge_tracepoint.h:24:29: warning: 'strncpy' output may be truncated copying 16 bytes from a string of length 20 [-Wstringop-truncation]
      24 |                             strncpy(__entry->dev_name,
         |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~
      25 |                                     netdev_name(fdb->dev),
         |                                     ~~~~~~~~~~~~~~~~~~~~~~
      26 |                                     IFNAMSIZ);
         |                                     ~~~~~~~~~

This is caused by the fact that default value of IFNAMSIZ is 16, while
placeholder value that is returned by netdev_name() for unnamed net devices
is larger than that.

The offending code is in a tracing function that is only called for mlx5
representors, so there is no straightforward way to reproduce the issue but
let's fix it for correctness sake by replacing strncpy() with strscpy() to
ensure that resulting string is always null-terminated.

Fixes: 9724fd5d

 ("net/mlx5: Bridge, add tracepoints")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>