RDMA/mlx5: Fix flow destination setting for RDMA TX flow table

For RDMA TX flow table, set destination type to be 'port' and prevent
creation of flows with TIR destination.

As RDMA TX is an egress flow table the rules on this flow table should
not forward traffic back to the NIC and should set the destination to be
the port.

Without the setting of this destination type flow rules on the RDMA TX
flow tables are not created as FW invokes a syndrome for undefined
destination for the rule.

Fixes: 24670b1a

 ("net/mlx5: Add support for RDMA TX steering")
Link: https://lore.kernel.org/r/20200803055849.14947-1-leon@kernel.org
Signed-off-by: Michael Guralnik <michaelgur@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>