Revert "net: Do not fill legacy info_str for backends"

Several issues has been reported for query-netdev info
series. Consider it's late in the rc, this reverts commit
f2e8319d45.

Signed-off-by: Jason Wang <jasowang@redhat.com>

net/vhost-user.c

@@ -327,6 +327,7 @@ static int net_vhost_user_init(NetClientState *peer, const char *device,
     user = g_new0(struct VhostUserState, 1);
     for (i = 0; i < queues; i++) {
         nc = qemu_new_net_client(&net_vhost_user_info, peer, device, name);
+        nc->info_str = g_strdup_printf("vhost-user%d to %s", i, chr->label);
         nc->queue_index = i;
         if (!nc0) {
             nc0 = nc;