selftests/bpf: Remove the only use of deprecated bpf_object__load_xattr()

Switch from bpf_object__load_xattr() to bpf_object__load() and
kernel_log_level in bpf_object_open_opts.

Signed-off-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/testing_helpers.c

···
 int bpf_prog_test_load(const char *file, enum bpf_prog_type type,
 		       struct bpf_object **pobj, int *prog_fd)
 {
-	struct bpf_object_load_attr attr = {};
+	LIBBPF_OPTS(bpf_object_open_opts, opts,
+		.kernel_log_level = extra_prog_load_log_flags,
+	);
 	struct bpf_object *obj;
 	struct bpf_program *prog;
 	__u32 flags;
 	int err;
 
-	obj = bpf_object__open(file);
+	obj = bpf_object__open_file(file, &opts);
 	if (!obj)
 		return -errno;
 
···
 	flags = bpf_program__flags(prog) | BPF_F_TEST_RND_HI32;
 	bpf_program__set_flags(prog, flags);
 
-	attr.obj = obj;
-	attr.log_level = extra_prog_load_log_flags;
-	err = bpf_object__load_xattr(&attr);
+	err = bpf_object__load(obj);
 	if (err)
 		goto err_out;