libbpf: Add bpf_object__token_fd accessor

Add a LIBBPF_API function to retrieve the token_fd from a bpf_object.

Without this accessor, if user needs a token FD they have to get it
manually via bpf_token_create, even though a token might have been
already created by bpf_object__load.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Ihor Solodrai <ihor.solodrai@pm.me>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240913001858.3345583-1-ihor.solodrai@pm.me

src/libbpf.c

@@ -9059,6 +9059,11 @@ unsigned int bpf_object__kversion(const struct bpf_object *obj)
 	return obj ? obj->kern_version : 0;
 }
 
+int bpf_object__token_fd(const struct bpf_object *obj)
+{
+	return obj->token_fd ?: -1;
+}
+
 struct btf *bpf_object__btf(const struct bpf_object *obj)
 {
 	return obj ? obj->btf : NULL;