ipv6: fix kabi for ip6_rt_gc_expire in struct netns_ipv6

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ISAH



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Making ip6_rt_gc_expire atomic breaks the KABI of struct netns_ipv6.
This patch uses KABI_REPLACE to fix it.

Signed-off-by: Xu Jia <xujia39@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>