net/mlx5: fs, Command to control L2TABLE entry silent mode

Introduce an API to set/unset the L2TABLE entry silent mode for a
device. If silent, no north/south traffic is allowed, the device won't
be able to communicate with the port directly to send/receive traffic by
its own.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>