tools: ynl: add sample for devlink

Add a sample to show off how to issue basic devlink requests.
For added testing issue get requests while walking a dump.

$ ./devlink
netdevsim/netdevsim1:
    driver: netdevsim
    running fw:
        fw.mgmt: 10.20.30
    ...
netdevsim/netdevsim2:
    driver: netdevsim
    running fw:
        fw.mgmt: 10.20.30
    ...
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/samples/.gitignore

+devlink
 netdev

tools/net/ynl/samples/devlink.c

+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <string.h>
+
+#include <ynl.h>
+
+#include "devlink-user.h"
+
+int main(int argc, char **argv)
+{
+	struct devlink_get_list *devs;
+	struct ynl_sock *ys;
+
+	ys = ynl_sock_create(&ynl_devlink_family, NULL);
+	if (!ys)
+		return 1;
+
+	devs = devlink_get_dump(ys);
+	if (!devs)
+		goto err_close;
+
+	ynl_dump_foreach(devs, d) {
+		struct devlink_info_get_req *info_req;
+		struct devlink_info_get_rsp *info_rsp;
+
+		printf("%s/%s:\n", d->bus_name, d->dev_name);
+
+		info_req = devlink_info_get_req_alloc();
+		devlink_info_get_req_set_bus_name(info_req, d->bus_name);
+		devlink_info_get_req_set_dev_name(info_req, d->dev_name);
+
+		info_rsp = devlink_info_get(ys, info_req);
+		devlink_info_get_req_free(info_req);
+		if (!info_rsp)
+			goto err_free_devs;
+
+		if (info_rsp->_present.info_driver_name_len)
+			printf("    driver: %s\n", info_rsp->info_driver_name);
+		if (info_rsp->n_info_version_running)
+			printf("    running fw:\n");
+		for (unsigned i = 0; i < info_rsp->n_info_version_running; i++)
+			printf("        %s: %s\n",
+			       info_rsp->info_version_running[i].info_version_name,
+			       info_rsp->info_version_running[i].info_version_value);
+		printf("    ...\n");
+		devlink_info_get_rsp_free(info_rsp);
+	}
+	devlink_get_list_free(devs);
+
+	ynl_sock_destroy(ys);
+
+	return 0;
+
+err_free_devs:
+	devlink_get_list_free(devs);
+err_close:
+	fprintf(stderr, "YNL: %s\n", ys->err.msg);
+	ynl_sock_destroy(ys);
+	return 2;
+}