ath79: ag71xx: add support for timer functions in linux 4.15+

Kernel newer than 4.15 dropped "data" field and used from_timer
to cast out the parent struct pointer for current timer.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>

target/linux/ath79/files/drivers/net/ethernet/atheros/ag71xx/ag71xx_main.c

@@ -985,10 +985,16 @@ static int ag71xx_do_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 	return -EOPNOTSUPP;
 }
 
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(4,15,0))
 static void ag71xx_oom_timer_handler(unsigned long data)
 {
 	struct net_device *dev = (struct net_device *) data;
 	struct ag71xx *ag = netdev_priv(dev);
+#else
+static void ag71xx_oom_timer_handler(struct timer_list *t)
+{
+	struct ag71xx *ag = from_timer(ag, t, oom_timer);
+#endif
 
 	napi_schedule(&ag->napi);
 }
@@ -1401,9 +1407,13 @@ static int ag71xx_probe(struct platform_device *pdev)
 
 	INIT_DELAYED_WORK(&ag->restart_work, ag71xx_restart_work_func);
 
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(4,15,0))
 	init_timer(&ag->oom_timer);
 	ag->oom_timer.data = (unsigned long) dev;
 	ag->oom_timer.function = ag71xx_oom_timer_handler;
+#else
+	timer_setup(&ag->oom_timer, ag71xx_oom_timer_handler, 0);
+#endif
 
 	tx_size = AG71XX_TX_RING_SIZE_DEFAULT;
 	ag->rx_ring.order = ag71xx_ring_size_order(AG71XX_RX_RING_SIZE_DEFAULT);