We must initialize prune_proxy_timer before we attempt
a del_timer_sync() on it.

syzbot reported the following splat:

INFO: trying to register non-static key.
The code is fine but needs lockdep annotation, or maybe
you didn't initialize this object before use?
turning off the locking correctness validator.
CPU: 1 PID: 11 Comm: kworker/u8:1 Not tainted 6.9.0-rc5-syzkaller-01199-gfc48de77 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: netns cleanup_net
Call Trace:
 <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
  assign_lock_key+0x238/0x270 kernel/locking/lockdep.c:976
  register_lock_class+0x1cf/0x980 kernel/locking/lockdep.c:1289
  __lock_acquire+0xda/0x1fd0 kernel/locking/lockdep.c:5014
  lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
  __timer_delete_sync+0x148/0x310 kernel/time/timer.c:1648
  del_timer_sync include/linux/timer.h:185 [inline]
  hsr_dellink+0x33/0x80 net/hsr/hsr_netlink.c:132
  default_device_exit_batch+0x956/0xa90 net/core/dev.c:11737
  ops_exit_list net/core/net_namespace.c:175 [inline]
  cleanup_net+0x89d/0xcc0 net/core/net_namespace.c:637
  process_one_work kernel/workqueue.c:3254 [inline]
  process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335
  worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
  kthread+0x2f0/0x390 kernel/kthread.c:388
  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
ODEBUG: assert_init not available (active state 0) object: ffff88806d3fcd88 object type: timer_list hint: 0x0
 WARNING: CPU: 1 PID: 11 at lib/debugobjects.c:517 debug_print_object+0x17a/0x1f0 lib/debugobjects.c:514

Fixes: 5055cccf ("net: hsr: Provide RedBox support (HSR-SAN)")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240426163355.2613767-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>