RDMA/srp: Rename SRP sysfs name after IB device rename trigger

RDMA/srp: Rename SRP sysfs name after IB device rename trigger

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: d21943dd19b5 ("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>