RDMA/mlx5: Allocate IB device with net namespace supplied from core dev

RDMA/mlx5: Allocate IB device with net namespace supplied from core dev

Use the new ib_alloc_device_with_net() API to allocate the IB device
so that it is properly bound to the network namespace obtained via
mlx5_core_net(). This change ensures correct namespace association
(e.g., for containerized setups).

Additionally, expose mlx5_core_net so that RDMA driver can use it.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>