net: lwip: rename linkoutput() as net_lwip_tx()

Rename static function linkoutput() as net_lwip_tx() for consistency
with net_lwip_rx().

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/net/lwip/net-lwip.c b/net/lwip/net-lwip.c
index cab1dd7..5a2a866 100644
--- a/net/lwip/net-lwip.c
+++ b/net/lwip/net-lwip.c
@@ -30,7 +30,7 @@
 struct in_addr	net_ip;
 char net_boot_file_name[1024];
 
-static err_t linkoutput(struct netif *netif, struct pbuf *p)
+static err_t net_lwip_tx(struct netif *netif, struct pbuf *p)
 {
 	struct udevice *udev = netif->state;
 	void *pp = NULL;
@@ -60,7 +60,7 @@
 static err_t net_lwip_if_init(struct netif *netif)
 {
 	netif->output = etharp_output;
-	netif->linkoutput = linkoutput;
+	netif->linkoutput = net_lwip_tx;
 	netif->mtu = 1500;
 	netif->flags = NETIF_FLAG_BROADCAST | NETIF_FLAG_ETHARP | NETIF_FLAG_LINK_UP;