IB/mlx5: Enable ECN capable bits for UD RoCE v2 QPs

When working with RC QPs, the FW sets the ECN capable bits for all
the RoCE v2 packets. On the other hand, for UD QPs, the driver needs
to set the the ECN capable bits in the Address Handler since the HW
generates each packet according to the Address Handler and not
the QP context.

If ECN is not enabled in NIC or switch, these bits are ignored.

Fixes: 2811ba51 ("IB/mlx5: Add RoCE fields to Address Vector")
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>