RDMA/mlx5: Allow inserting a steering rule to the FDB

Allow this only via mlx5 raw create flow API, legacy verbs are not
supported. To accommodate that, we add a new attribute to matcher creation
to indicate the type of flow table to be used.
	MLX5_IB_ATTR_FLOW_MATCHER_FT_TYPE
With this new attribute MLX5_IB_ATTR_FLOW_MATCHER_FLOW_FLAGS is no longer
needed, we keep it for compatibility but at most only a single attribute can
be passed of the two.

When inserting a flow rule to the FDB we require that a DEVX FT is
provided as a destination, no other configuration is allowed.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>