ipv6: delay fib6_sernum increase in fib6_add

stable inclusion
from stable-5.10.70
commit 9561bb98879e45c49c18b6b54ca9f6e36393edc8
bugzilla: 182949 https://gitee.com/openeuler/kernel/issues/I4I3GQ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9561bb98879e45c49c18b6b54ca9f6e36393edc8

--------------------------------

[ Upstream commit e87b5052 ]

only increase fib6_sernum in net namespace after add fib6_info
successfully.
Signed-off-by: Nzhang kai <zhangkaiheb@126.com>
Reviewed-by: NDavid Ahern <dsahern@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

net/ipv6/ip6_fib.c

@@ -1377,7 +1377,6 @@ int fib6_add(struct fib6_node *root, struct fib6_info *rt,
 	int err = -ENOMEM;
 	int allow_create = 1;
 	int replace_required = 0;
-	int sernum = fib6_new_sernum(info->nl_net);
 
 	if (info->nlh) {
 		if (!(info->nlh->nlmsg_flags & NLM_F_CREATE))
@@ -1477,7 +1476,7 @@ int fib6_add(struct fib6_node *root, struct fib6_info *rt,
 	if (!err) {
 		if (rt->nh)
 			list_add(&rt->nh_list, &rt->nh->f6i_list);
-		__fib6_update_sernum_upto_root(rt, sernum);
+		__fib6_update_sernum_upto_root(rt, fib6_new_sernum(info->nl_net));
 		fib6_start_gc(info->nl_net, rt);
 	}