SRP logic used device name and port index as symlink to relevant
kobject. If the IB device is renamed then the prior name will be re-used
by the next device plugged in and sysfs will panic as SRP will try to
re-use the same name.

 mlx5_ib: Mellanox Connect-IB Infiniband driver v5.0-0
 sysfs: cannot create duplicate filename '/class/infiniband_srp/srp-mlx5_0-1'
 CPU: 3 PID: 1107 Comm: modprobe Not tainted 5.1.0-for-upstream-perf-2019-05-12_15-09-52-87 #1
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
 Call Trace:
  dump_stack+0x5a/0x73
  sysfs_warn_dup+0x58/0x70
  sysfs_do_create_link_sd.isra.2+0xa3/0xb0
  device_add+0x33f/0x660
  srp_add_one+0x301/0x4f0 [ib_srp]
  add_client_context+0x99/0xe0 [ib_core]
  enable_device_and_get+0xd1/0x1b0 [ib_core]
  ib_register_device+0x533/0x710 [ib_core]
  ? mutex_lock+0xe/0x30
  __mlx5_ib_add+0x23/0x70 [mlx5_ib]
  mlx5_add_device+0x4e/0xd0 [mlx5_core]
  mlx5_register_interface+0x85/0xc0 [mlx5_core]
  ? 0xffffffffa0791000
  do_one_initcall+0x4b/0x1cb
  ? kmem_cache_alloc_trace+0xc6/0x1d0
  ? do_init_module+0x22/0x21f
  do_init_module+0x5a/0x21f
  load_module+0x17f2/0x1ca0
  ? m_show+0x1c0/0x1c0
  __do_sys_finit_module+0x94/0xe0
  do_syscall_64+0x48/0x120
  entry_SYSCALL_64_after_hwframe+0x44/0xa9
 RIP: 0033:0x7f157cce10d9

The module load/unload sequence was used to trigger such kernel panic:
 sudo modprobe ib_srp
 sudo modprobe -r mlx5_ib
 sudo modprobe -r mlx5_core
 sudo modprobe mlx5_core

Have SRP track the name of the core device so that it can't have a name
collision.

Fixes: d21943dd ("RDMA/core: Implement IB device rename function")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>