livepatch/ppc64: Ignore the first frame when checking stack

rtos inclusion
category: bugfix
bugzilla: 42399/46793/51924
CVE: NA

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According to function _switch in entry_32/64.S, for non-current and
not-in-interrupt task, the LR is saved in the LR position in the 2nd
frame. The content in LR position in the 1st frame is not filled, so
it is left by previous stack frames and may be an address in a kernel
function, resulting in failure in applying a kernel patch even when the
target function is not actually in stack.

Therefore, we should ignore the first frame to get a more reliable
backtrace.

Signed-off-by: Lexi Shao <shaolexi@huawei.com>
Reviewed-by: Cheng Jian <cj.chengjian@huawei.com>
Signed-off-by: yangerkun <yangerkun@huawei.com>

Signed-off-by: Dong Kai <dongkai11@huawei.com>

Signed-off-by: Ye Weihua <yeweihua4@huawei.com>
Reviewed-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>