RDMA/mlx5: Fix legacy IPoIB QP initialization

Legacy IPoIB sets IB_QP_CREATE_NETIF_QP QP create flag and because mlx5
doesn't use this flag, the process_create_flags() failed to create IPoIB
QPs.

Fixes: 2978975c

 ("RDMA/mlx5: Process create QP flags in one place")
Link: https://lore.kernel.org/r/20200630122147.445847-1-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>