libbpf: Add support to create tracing multi link

libbpf: Add support to create tracing multi link

Adding bpf_program__attach_tracing_multi function for attaching
tracing program to multiple functions.

  struct bpf_link *
  bpf_program__attach_tracing_multi(const struct bpf_program *prog,
                                    const char *pattern,
                                    const struct bpf_tracing_multi_opts *opts);

User can specify functions to attach with 'pattern' argument that
allows wildcards (*?' supported) or provide BTF ids of functions
in array directly via opts argument. These options are mutually
exclusive.

When using BTF ids, user can also provide cookie value for each
provided id/function, that can be retrieved later in bpf program
with bpf_get_attach_cookie helper. Each cookie value is paired with
provided BTF id with the same array index.

Adding support to auto attach programs with following sections:

  fsession.multi/<pattern>
  fsession.multi.s/<pattern>
  fentry.multi/<pattern>
  fexit.multi/<pattern>
  fentry.multi.s/<pattern>
  fexit.multi.s/<pattern>

The provided <pattern> is used as 'pattern' argument in
bpf_program__attach_kprobe_multi_opts function.

The <pattern> allows to specify optional kernel module name with
following syntax:

  <module>:<function_pattern>

In order to attach tracing_multi link to a module functions:
- program must be loaded with 'module' btf fd
  (in attr::attach_btf_obj_fd)
- bpf_program__attach_tracing_multi must either have
  pattern with module spec or BTF ids from the module

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20260606123955.345967-21-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>