mm/vmscan: fix unexpected shrinking page cache with vm_cache_reclaim_enable disable

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SK3S


CVE: NA

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In function cache_limit_ratio_sysctl_handler and
cache_limit_mbytes_sysctl_handler, it will shrink
page cache even if vm_cache_reclaim_enable is false,
it is unexpected.

Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>