livepatch/arm64: fix func size less than limit

euler inclusion
category: feature
Bugzilla: 5507
CVE: N/A

----------------------------------------

we need to modify the first 4 instructions of a livepatch function to
complete the long jump if offset out of short-range. So it's important
that this function must have more than 4 instructions, so we checked it
when the livepatch module insmod.

In fact, this corner case is highly unlikely tooccur on arm64, but it's
still an effective and meaningful check to avoid crash by doing this.

Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
Reviewed-by: Li Bin <huawei.libin@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>