ethtool-util: make wol_options_to_string() not return all flag strings

src/shared/ethtool-util.c

@@ -43,6 +43,11 @@ int wol_options_to_string_alloc(uint32_t opts, char **ret) {
 
         assert(ret);
 
+        if (opts == UINT32_MAX) {
+                *ret = NULL;
+                return 0;
+        }
+
         for (size_t i = 0; i < ELEMENTSOF(wol_option_map); i++)
                 if (opts & wol_option_map[i].opt &&
                     !strextend_with_separator(&str, ",", wol_option_map[i].name))
@@ -55,7 +60,7 @@ int wol_options_to_string_alloc(uint32_t opts, char **ret) {
         }
 
         *ret = TAKE_PTR(str);
-        return 0;
+        return 1;
 }
 
 static const char* const port_table[] = {

src/udev/net/link-config.c

@@ -334,8 +334,8 @@ static int link_config_apply_ethtool_settings(int *ethtool_fd, const LinkConfig
                 _cleanup_free_ char *str = NULL;
 
                 (void) wol_options_to_string_alloc(config->wol, &str);
-                log_device_warning_errno(device, r, "Could not set WakeOnLan to %s, ignoring: %m",
-                                         strna(str));
+                log_device_warning_errno(device, r, "Could not set WakeOnLan%s%s, ignoring: %m",
+                                         isempty(str) ? "" : " to ", strempty(str));
         }
 
         r = ethtool_set_features(ethtool_fd, name, config->features);