selftests/bpf: Test re-attachment fix for bpf_tracing_prog_attach

Add a test case to verify the fix for "prog->aux->dst_trampoline and
tgt_prog is NULL" branch in bpf_tracing_prog_attach. The sequence of
events:

1. load rawtp program
2. load fentry program with rawtp as target_fd
3. create tracing link for fentry program with target_fd = 0
4. repeat 3

Acked-by: Jiri Olsa <olsajiri@gmail.com>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
Link: https://lore.kernel.org/r/20240103190559.14750-5-9erthalion6@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>