kabi: reserve space for cred and user_namespace

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4MYYH
CVE: N/A

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

Reserve space in struct cred and struct user_namespace in advance to
prepare for merging a promising new feature [1] from kernel 5.14 and
some others in the future.

[1]: https://lkml.kernel.org/r/94d1dbecab060a6b116b0a2d1accd8ca1bbb4f5f.1619094428.git.legion@kernel.org



Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: weiyang wang <wangweiyang2@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>