rdma: Print net device name and index for RDMA device

rdma: Print net device name and index for RDMA device

The RDMA devices are operated in RoCE and iWARP modes have net device
underneath. Present their names in regular output and their net index
in detailed mode.

[root@nps ~]# rdma link show mlx5_3/1
4/1: mlx5_3/1: state ACTIVE physical_state LINK_UP netdev ens7
[root@nps ~]# rdma link show mlx5_3/1 -d
4/1: mlx5_3/1: state ACTIVE physical_state LINK_UP netdev ens7 netdev_index 7
    caps: <CM, IP_BASED_GIDS>

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: David Ahern <dsahern@gmail.com>