selftests/bpf: Add few corner cases to test padding handling of btf_dump

stable inclusion
from stable-v5.10.177
commit 7ad30ad8c684362364e629574ab02eec3b9bb1bc
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I88YNP

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7ad30ad8c684362364e629574ab02eec3b9bb1bc

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[ Upstream commit b148c8b9 ]

Add few hand-crafted cases and few randomized cases found using script
from [0] that tests btf_dump's padding logic.

  [0] https://lore.kernel.org/bpf/85f83c333f5355c8ac026f835b18d15060725fcb.camel@ericsson.com/



Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20221212211505.558851-7-andrii@kernel.org


Stable-dep-of: 4fb877aa ("libbpf: Fix btf_dump's packed struct determination")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>