kabi: reserve space for net_namespace

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4KKML


DTS: NA
CVE: NA

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Reserve space in net_namespace.h

Signed-off-by: Cui GaoSheng <cuigaosheng1@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>