net/proxy: stop updating netdev->last_rx with kernel 4.11+

The network stack stopped using netdev->last_rx a long time ago, and
this field was removed during the 4.11 development cycle
(#4a7c972644c1).

kernel/drivers/net/addons/proxy.c

@@ -256,7 +256,9 @@ static inline void rtnetproxy_kernel_recv(struct rtskb *rtskb)
     /* the rtskb stamp is useless (different clock), get new one */
     __net_timestamp(skb);
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4,11,0)
     dev->last_rx = jiffies;
+#endif
     dev->stats.rx_bytes+=skb->len;
     dev->stats.rx_packets++;