bpf: add bpf_probe_read_str into bpf_helpers.h

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I3UHF8


CVE: NA

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Then, we can use bpf_probe_read_str() into ebpf program.

Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>