ethtool: make ethtool_get_driver() return -ENODATA if ioctl succeeds but driver name is empty

Inspired by #17532.

src/shared/ethtool-util.c

@@ -197,6 +197,9 @@ int ethtool_get_driver(int *ethtool_fd, const char *ifname, char **ret) {
         if (r < 0)
                 return -errno;
 
+        if (isempty(ecmd.driver))
+                return -ENODATA;
+
         d = strdup(ecmd.driver);
         if (!d)
                 return -ENOMEM;