livepatch/x86: Rename old_code to old_insns

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60L10


CVE: NA

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In arm/arm64/ppc32/ppc64, this field is named as old_insns, so uniform it.

Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>