mm: Update reliable flag in memory allocaion for reliable task only in task context

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


CVE: NA

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Since interrupt may occupy reliable task's context and its current->flags
will have PF_RELIABLE and this will lead to redirect it's memory allocation
to mirrored region.

Update reliable task's gfp flag can only happen in normal task context by
checking in_task().

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>