livepatch: Bypass dead thread when check calltrace

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8MGE6



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When the thread become zombie or dead, it's stack memory may
have been freed, so ignore it.

Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>