IB/mlx5: When not in dual port RoCE mode, use provided port as native

The series that introduced dual port RoCE mode assumed that we don't have
a dual port HCA that use the mlx5 driver, this is not the case for
Connect-IB HCAs. This reasoning led to assigning 1 as the native port
index which causes issue when the second port is used.

For example query_pkey() when called on the second port will return values
of the first port. Make sure that we assign the right port index as the
native port index.

Fixes: 32f69e4b ("{net, IB}/mlx5: Manage port association for multiport RoCE")
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>