mwifiex: set valid tx_param during mwifiex_send_null_packet

While sending null packet from driver we are passing NULL
tx_param pointer to indicate there are no more packets in queue.
PCIe send routine assumes caller has done sanity check on
tx_param and may cause crash while dereferencing next_pkt_len
from tx_param.

Avoid this by passing tx_param structure with next_pkt_len as
zero instead of NULL pointer.
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/mwifiex/pcie.c

@@ -1071,6 +1071,7 @@ static int mwifiex_pcie_send_data_complete(struct mwifiex_adapter *adapter)
  * is mapped to PCI device memory. Tx ring pointers are advanced accordingly.
  * Download ready interrupt to FW is deffered if Tx ring is not full and
  * additional payload can be accomodated.
+ * Caller must ensure tx_param parameter to this function is not NULL.
  */
 static int
 mwifiex_pcie_send_data(struct mwifiex_adapter *adapter, struct sk_buff *skb,

drivers/net/wireless/mwifiex/sta_tx.c

@@ -128,6 +128,7 @@ int mwifiex_send_null_packet(struct mwifiex_private *priv, u8 flags)
 {
 	struct mwifiex_adapter *adapter = priv->adapter;
 	struct txpd *local_tx_pd;
+	struct mwifiex_tx_param tx_param;
 /* sizeof(struct txpd) + Interface specific header */
 #define NULL_PACKET_HDR 64
 	u32 data_len = NULL_PACKET_HDR;
@@ -168,8 +169,9 @@ int mwifiex_send_null_packet(struct mwifiex_private *priv, u8 flags)
 						   skb, NULL);
 	} else {
 		skb_push(skb, INTF_HEADER_LEN);
+		tx_param.next_pkt_len = 0;
 		ret = adapter->if_ops.host_to_card(adapter, MWIFIEX_TYPE_DATA,
-						   skb, NULL);
+						   skb, &tx_param);
 	}
 	switch (ret) {
 	case -EBUSY: