vhost-user: add get_vhost_net() assertions

Add a few assertions to be more explicit about the runtime behaviour
after the previous patch: get_vhost_net() is non-null after
net_vhost_user_init().

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/net/vhost_net.c

@@ -417,6 +417,7 @@ VHostNetState *get_vhost_net(NetClientState *nc)
         break;
     case NET_CLIENT_DRIVER_VHOST_USER:
         vhost_net = vhost_user_get_vhost_net(nc);
+        assert(vhost_net);
         break;
     default:
         break;

net/vhost-user.c

@@ -259,6 +259,8 @@ static int net_vhost_user_init(NetClientState *peer, const char *device,
 
     qemu_chr_add_handlers(chr, NULL, NULL, net_vhost_user_event, nc[0].name);
 
+    assert(s->vhost_net);
+
     return 0;
 }