qlcnic: underflow in qlcnic_validate_max_tx_rings()

This function checks the upper bound but it doesn't check for negative
numbers:

	if (txq > QLCNIC_MAX_TX_RINGS) {

I've solved this by making "txq" a u32 type.  I chose that because
->tx_count in the ethtool_channels struct is a __u32.

This bug was added in aa4a1f7df7 ('qlcnic: Enable Tx queue changes using
ethtool for 82xx Series adapter.').

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qlogic/qlcnic/qlcnic.h

@@ -1542,7 +1542,7 @@ int qlcnic_diag_alloc_res(struct net_device *netdev, int test);
 netdev_tx_t qlcnic_xmit_frame(struct sk_buff *skb, struct net_device *netdev);
 int qlcnic_set_max_rss(struct qlcnic_adapter *, u8, int);
 int qlcnic_validate_max_rss(struct qlcnic_adapter *, __u32);
-int qlcnic_validate_max_tx_rings(struct qlcnic_adapter *, int);
+int qlcnic_validate_max_tx_rings(struct qlcnic_adapter *, u32 txq);
 void qlcnic_alloc_lb_filters_mem(struct qlcnic_adapter *adapter);
 void qlcnic_82xx_set_mac_filter_count(struct qlcnic_adapter *);
 int qlcnic_enable_msix(struct qlcnic_adapter *, u32);

drivers/net/ethernet/qlogic/qlcnic/qlcnic_main.c

@@ -3548,7 +3548,7 @@ qlcnicvf_start_firmware(struct qlcnic_adapter *adapter)
 	return err;
 }
 
-int qlcnic_validate_max_tx_rings(struct qlcnic_adapter *adapter, int txq)
+int qlcnic_validate_max_tx_rings(struct qlcnic_adapter *adapter, u32 txq)
 {
 	struct net_device *netdev = adapter->netdev;
 	u8 max_hw = QLCNIC_MAX_TX_RINGS;