net: Add vhost-vdpa in show_netdevs()

Fix the bug that while Check qemu supported netdev,
there is no vhost-vdpa

Signed-off-by: Cindy Lu <lulu@redhat.com>
Message-Id: <20201016030909.9522-2-lulu@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/net/net.c b/net/net.c
index 7a2a0fb..794c652 100644
--- a/net/net.c
+++ b/net/net.c
@@ -1050,6 +1050,9 @@
 #ifdef CONFIG_POSIX
         "vhost-user",
 #endif
+#ifdef CONFIG_VHOST_VDPA
+        "vhost-vdpa",
+#endif
     };
 
     printf("Available netdev backend types:\n");