selftests/bpf: Free the allocated resources after test case succeeds

Free the created fd or allocated bpf_object after test case succeeds,
else there will be resource leaks.

Spotted by using address sanitizer and checking the content of
/proc/$pid/fd directory.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20220921070035.2016413-3-houtao@huaweicloud.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>