IB/mlx5: Add support for a flow table destination for driver flow steering

Add support to set a destination that is a flow table, this can come from
the DEVX destination.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>