ath9k: Reintroduce modparam to enable btcoex

It is not ideal to enable btcoex based on subsys id as it is
not unique, they are so random. It is also a pain keeping
all of them in a table to enable btcoex for a particular
hw. Going back to the old idea.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath.h b/drivers/net/wireless/ath/ath.h
index 20ea68c..26bdbee 100644
--- a/drivers/net/wireless/ath/ath.h
+++ b/drivers/net/wireless/ath/ath.h
@@ -168,6 +168,8 @@
 	struct ath_regulatory regulatory;
 	const struct ath_ops *ops;
 	const struct ath_bus_ops *bus_ops;
+
+	bool btcoex_enabled;
 };
 
 struct sk_buff *ath_rxbuf_alloc(struct ath_common *common,