unregister_netdevice: waiting for lo to become free. Usage count = 2
leaked reference.
 __netdev_tracker_alloc include/linux/netdevice.h:4020 [inline]
 netdev_hold include/linux/netdevice.h:4049 [inline]
 ipv6_add_dev+0x3c1/0x1160 net/ipv6/addrconf.c:401
 addrconf_notify+0x464/0x1340 net/ipv6/addrconf.c:3552
 notifier_call_chain+0x94/0x170 kernel/notifier.c:87
 call_netdevice_notifiers_extack net/core/dev.c:1982 [inline]
 call_netdevice_notifiers net/core/dev.c:1996 [inline]
 register_netdevice+0xcc1/0x1400 net/core/dev.c:10078
 register_netdev+0x1b/0x40 net/core/dev.c:10173
 loopback_net_init+0x70/0x130 drivers/net/loopback.c:219
 ops_init+0x96/0x580 net/core/net_namespace.c:135
 setup_net+0x74a/0xd60 net/core/net_namespace.c:333
 copy_net_ns+0x2a8/0x540 net/core/net_namespace.c:483
 create_new_namespaces+0x35a/0x920 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0x8a/0x1a0 kernel/nsproxy.c:228
 ksys_unshare+0x30d/0x6b0 kernel/fork.c:3202
 __do_sys_unshare kernel/fork.c:3273 [inline]
 __se_sys_unshare kernel/fork.c:3271 [inline]
 __x64_sys_unshare+0x2c/0x40 kernel/fork.c:3271
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd