net/mlx5: Lag, Add single RDMA device in multiport mode

In MultiPort E-Switch mode a single RDMA is created. This device has multiple
RDMA ports that represent the uplink ports that are connected to the E-Switch.
Account for this when creating the RDMA device so it has an additional port for
the non native uplink.

As a side effect of this patch, use shared fdb in multiport eswitch mode.

Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>