vhost-user: disconnect on start failure

If the backend failed to start (for example feature negociation failed),
do not exit, but disconnect the char device instead. Slightly more
robust for reconnect case.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: NYuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: NYuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: NVictor Kaplansky <victork@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

net/vhost-user.c

@@ -202,7 +202,8 @@ static void net_vhost_user_event(void *opaque, int event)
         s->watch = qemu_chr_fe_add_watch(s->chr, G_IO_HUP,
                                          net_vhost_user_watch, s);
         if (vhost_user_start(queues, ncs) < 0) {
-            exit(1);
+            qemu_chr_disconnect(s->chr);
+            return;
         }
         qmp_set_link(name, true, &err);
         break;