selftests/bpf: Add test case for element reuse in htab map

The reinitialization of spin-lock in map value after immediate reuse may
corrupt lookup with BPF_F_LOCK flag and result in hard lock-up, so add
one test case to demonstrate the problem.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20230215082132.3856544-3-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>