ipv6: fix WARNING in ip6_route_net_exit_late()

During the initialization of ip6_route_net_init_late(), if file
ipv6_route or rt6_stats fails to be created, the initialization is
successful by default. Therefore, the ipv6_route or rt6_stats file
doesn't be found during the remove in ip6_route_net_exit_late(). It
will cause WRNING.

The following is the stack information:
name 'rt6_stats'
WARNING: CPU: 0 PID: 9 at fs/proc/generic.c:712 remove_proc_entry+0x389/0x460
Modules linked in:
Workqueue: netns cleanup_net
RIP: 0010:remove_proc_entry+0x389/0x460
PKRU: 55555554
Call Trace:
<TASK>
ops_exit_list+0xb0/0x170
cleanup_net+0x4ea/0xb00
process_one_work+0x9bf/0x1710
worker_thread+0x665/0x1080
kthread+0x2e4/0x3a0
ret_from_fork+0x1f/0x30
</TASK>

Fixes: cdb18761 ("[NETNS][IPV6] route6 - create route6 proc files for the namespace")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20221102020610.351330-1-shaozhengchao@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/route.c

@@ -6555,10 +6555,16 @@ static void __net_exit ip6_route_net_exit(struct net *net)
 static int __net_init ip6_route_net_init_late(struct net *net)
 {
 #ifdef CONFIG_PROC_FS
-	proc_create_net("ipv6_route", 0, net->proc_net, &ipv6_route_seq_ops,
-			sizeof(struct ipv6_route_iter));
-	proc_create_net_single("rt6_stats", 0444, net->proc_net,
-			rt6_stats_seq_show, NULL);
+	if (!proc_create_net("ipv6_route", 0, net->proc_net,
+			     &ipv6_route_seq_ops,
+			     sizeof(struct ipv6_route_iter)))
+		return -ENOMEM;
+
+	if (!proc_create_net_single("rt6_stats", 0444, net->proc_net,
+				    rt6_stats_seq_show, NULL)) {
+		remove_proc_entry("ipv6_route", net->proc_net);
+		return -ENOMEM;
+	}
 #endif
 	return 0;
 }