virtio-devices: Add rate limiter for the RX queue of virtio-net

Fixes: #1286

Signed-off-by: Bo Chen <chen.bo@intel.com>

vhost_user_net/src/lib.rs

@@ -111,6 +111,8 @@ impl VhostUserNetThread {
                 epoll_fd: None,
                 counters: NetCounters::default(),
                 tap_event_id: 2,
+                rx_desc_avail: false,
+                rx_rate_limiter: None,
                 tx_rate_limiter: None,
             },
         })