iwlwifi: fix DMA channel number in iwl_txq_ctx_stop

The patch fixes the misuse of DMA channel number by Tx queue number in
iwl_tx_ctx_stop().

The problem was originally reported by Wu Fengguang who complains
iwlagn driver takes too long time when issuing `ifconfig wlan0 down`.
The patch now decreases the interface bring down time from 2 seconds
to 0.8 second.

This fixes bugs:
http://bugzilla.kernel.org/show_bug.cgi?id=11956
http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=1790

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-5000.c b/drivers/net/wireless/iwlwifi/iwl-5000.c
index b6c57cb..f7a8df8 100644
--- a/drivers/net/wireless/iwlwifi/iwl-5000.c
+++ b/drivers/net/wireless/iwlwifi/iwl-5000.c
@@ -827,6 +827,7 @@
 	}
 
 	priv->hw_params.max_txq_num = priv->cfg->mod_params->num_of_queues;
+	priv->hw_params.dma_chnl_num = FH50_TCSR_CHNL_NUM;
 	priv->hw_params.scd_bc_tbls_size =
 			IWL50_NUM_QUEUES * sizeof(struct iwl5000_scd_bc_tbl);
 	priv->hw_params.max_stations = IWL5000_STATION_COUNT;