qcacld-3.0: Fix -Wmissing-prototypes in wlan_hdd_tx_rx

We want to enable the compiler's -Wmissing-prototypes switch, but
there is existing code that is generating warnings. Fix all warnings
in wlan_hdd_tx_rx.

Change-Id: Ic1eaf337ff339e979c3f78e667be9539eb47f5dc
CRs-Fixed: 1074336

core/hdd/src/wlan_hdd_tx_rx.c

@@ -402,7 +402,7 @@ static void hdd_get_transmit_sta_id(hdd_adapter_t *adapter,
  *
  * Return: Always returns NETDEV_TX_OK
  */
-int __hdd_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static int __hdd_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	QDF_STATUS status;
 	sme_ac_enum_type ac;
@@ -1099,7 +1099,7 @@ static void wlan_hdd_update_queue_oper_stats(hdd_adapter_t *adapter,
  *
  * Return: none
  */
-void wlan_hdd_update_txq_timestamp(struct net_device *dev)
+static void wlan_hdd_update_txq_timestamp(struct net_device *dev)
 {
 	struct netdev_queue *txq;
 	int i;