selftests/bpf: Add test for bpf_timer overwriting crash

selftests/bpf: Add test for bpf_timer overwriting crash

[ Upstream commit a7e75016a0753c24d6c995bc02501ae35368e333 ]

Add a test that validates that timer value is not overwritten when doing
a copy_map_value call in the kernel. Without the prior fix, this test
triggers a crash.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220209070324.1093182-3-memxor@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>