net: lantiq_etop: Fix return type for implementation of ndo_start_xmit

Since Linux now supports CFI, it will be a good idea to fix mismatched
return type for implementation of hooks. Otherwise this might get
cought out by CFI and cause a panic.

ltq_etop_tx() would return either NETDEV_TX_BUSY or NETDEV_TX_OK, so
change the return type to netdev_tx_t directly.
Signed-off-by: GUO Zihua <guozihua@huawei.com>
Link: https://lore.kernel.org/r/20220902081521.59867-1-guozihua@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/lantiq_etop.c

@@ -470,7 +470,7 @@ ltq_etop_stop(struct net_device *dev)
 	return 0;
 }
 
-static int
+static netdev_tx_t
 ltq_etop_tx(struct sk_buff *skb, struct net_device *dev)
 {
 	int queue = skb_get_queue_mapping(skb);