libbpf: Add support for bpf iter in light skeleton.

bpf iterator programs should use bpf_link_create to attach instead of
bpf_raw_tracepoint_open like other tracing programs.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220131220528.98088-2-alexei.starovoitov@gmail.com

tools/bpf/bpftool/gen.c

@@ -384,7 +384,10 @@ static void codegen_attach_detach(struct bpf_object *obj, const char *obj_name)
 			printf("\tint fd = bpf_raw_tracepoint_open(\"%s\", prog_fd);\n", tp_name);
 			break;
 		case BPF_PROG_TYPE_TRACING:
-			printf("\tint fd = bpf_raw_tracepoint_open(NULL, prog_fd);\n");
+			if (bpf_program__expected_attach_type(prog) == BPF_TRACE_ITER)
+				printf("\tint fd = bpf_link_create(prog_fd, 0, BPF_TRACE_ITER, NULL);\n");
+			else
+				printf("\tint fd = bpf_raw_tracepoint_open(NULL, prog_fd);\n");
 			break;
 		default:
 			printf("\tint fd = ((void)prog_fd, 0); /* auto-attach not supported */\n");