vhost_net: cleanup start/stop condition

Checking vhost device internal state in vhost_net looks like
a layering violation since vhost_net does not
set this flag: it is set and tested by vhost.c.
There seems to be no reason to check this:
caller in virtio net uses its own flag,
vhost_started, to ensure vhost is started/stopped
as appropriate.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Amos Kong <akong@redhat.com>

hw/net/vhost_net.c

@@ -195,10 +195,6 @@ static int vhost_net_start_one(struct vhost_net *net,
     struct vhost_vring_file file = { };
     int r;
 
-    if (net->dev.started) {
-        return 0;
-    }
-
     net->dev.nvqs = 2;
     net->dev.vqs = net->vqs;
     net->dev.vq_index = vq_index;
@@ -256,10 +252,6 @@ static void vhost_net_stop_one(struct vhost_net *net,
 {
     struct vhost_vring_file file = { .fd = -1 };
 
-    if (!net->dev.started) {
-        return;
-    }
-
     if (net->nc->info->type == NET_CLIENT_OPTIONS_KIND_TAP) {
         for (file.index = 0; file.index < net->dev.nvqs; ++file.index) {
             const VhostOps *vhost_ops = net->dev.vhost_ops;