wl1251: fix channel switching in monitor mode

Use the ENABLE_RX command for channel switching when no interface is present
(monitor mode only).
The advantage of ENABLE_RX is that it leaves the tx data path disabled in
firmware, whereas the usual JOIN command seems to transmit some frames at
firmware level.
Signed-off-by: NDavid Gnedt <david.gnedt@davizone.at>
Signed-off-by: NPali Rohár <pali.rohar@gmail.com>
Signed-off-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ti/wl1251/main.c

@@ -615,8 +615,19 @@ static int wl1251_op_config(struct ieee80211_hw *hw, u32 changed)
 	if (channel != wl->channel) {
 		wl->channel = channel;
 
-		ret = wl1251_join(wl, wl->bss_type, wl->channel,
-				  wl->beacon_int, wl->dtim_period);
+		/*
+		 * Use ENABLE_RX command for channel switching when no
+		 * interface is present (monitor mode only).
+		 * This leaves the tx path disabled in firmware, whereas
+		 * the usual JOIN command seems to transmit some frames
+		 * at firmware level.
+		 */
+		if (wl->vif == NULL) {
+			ret = wl1251_cmd_data_path_rx(wl, wl->channel, 1);
+		} else {
+			ret = wl1251_join(wl, wl->bss_type, wl->channel,
+					  wl->beacon_int, wl->dtim_period);
+		}
 		if (ret < 0)
 			goto out_sleep;
 	}