bpf: test case for map pointer poison with calls/branches

Add several test cases where the same or different map pointers
originate from different paths in the program and execute a map
lookup or tail call at a common location.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>