net/mlx5: Bridge, Enable mcast in smfs steering mode

In order to have mcast offloads the driver needs the following:
It should know if that mcast comes from wire port, in addition the flow
should not be marked as any specific source, that way it will give the
flexibility for the driver not to be depended on the way iterator
implemented in the FW.

Signed-off-by: Erez Shitrit <erezsh@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>