um: net: Do not use drvdata in release

um: net: Do not use drvdata in release

The drvdata is not available in release. Let's just use container_of()
to get the uml_net instance. Otherwise, removing a network device will
result in a crash:

RIP: 0033:net_device_release+0x10/0x6f
RSP: 00000000e20c7c40  EFLAGS: 00010206
RAX: 000000006002e4e7 RBX: 00000000600f1baf RCX: 00000000624074e0
RDX: 0000000062778000 RSI: 0000000060551c80 RDI: 00000000627af028
RBP: 00000000e20c7c50 R08: 00000000603ad594 R09: 00000000e20c7b70
R10: 000000000000135a R11: 00000000603ad422 R12: 0000000000000000
R13: 0000000062c7af00 R14: 0000000062406d60 R15: 00000000627700b6
Kernel panic - not syncing: Segfault with no mm
CPU: 0 UID: 0 PID: 29 Comm: kworker/0:2 Not tainted 6.12.0-rc6-g59b723cd2adb #1
Workqueue: events mc_work_proc
Stack:
 627af028 62c7af00 e20c7c80 60276fcd
 62778000 603f5820 627af028 00000000
 e20c7cb0 603a2bcd 627af000 62770010
Call Trace:
 [<60276fcd>] device_release+0x70/0xba
 [<603a2bcd>] kobject_put+0xba/0xe7
 [<60277265>] put_device+0x19/0x1c
 [<60281266>] platform_device_put+0x26/0x29
 [<60281e5f>] platform_device_unregister+0x2c/0x2e
 [<6002ec9c>] net_remove+0x63/0x69
 [<60031316>] ? mconsole_reply+0x0/0x50
 [<600310c8>] mconsole_remove+0x160/0x1cc
 [<60087d40>] ? __remove_hrtimer+0x38/0x74
 [<60087ff8>] ? hrtimer_try_to_cancel+0x8c/0x98
 [<6006b3cf>] ? dl_server_stop+0x3f/0x48
 [<6006b390>] ? dl_server_stop+0x0/0x48
 [<600672e8>] ? dequeue_entities+0x327/0x390
 [<60038fa6>] ? um_set_signals+0x0/0x43
 [<6003070c>] mc_work_proc+0x77/0x91
 [<60057664>] process_scheduled_works+0x1b3/0x2dd
 [<60055f32>] ? assign_work+0x0/0x58
 [<60057f0a>] worker_thread+0x1e9/0x293
 [<6005406f>] ? set_pf_worker+0x0/0x64
 [<6005d65d>] ? arch_local_irq_save+0x0/0x2d
 [<6005d748>] ? kthread_exit+0x0/0x3a
 [<60057d21>] ? worker_thread+0x0/0x293
 [<6005dbf1>] kthread+0x126/0x12b
 [<600219c5>] new_thread_handler+0x85/0xb6

Cc: stable@vger.kernel.org
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Link: https://patch.msgid.link/20241104163203.435515-4-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>