ath10k: detect conf_mutex held ath10k_drain_tx() calls

ath10k_drain_tx() must not be called with conf_mutex held as workers can
use that also. Add check to detect conf_mutex held calls.

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

drivers/net/wireless/ath/ath10k/mac.c

@@ -4727,6 +4727,7 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw,
 /* Must not be called with conf_mutex held as workers can use that also. */
 void ath10k_drain_tx(struct ath10k *ar)
 {
+	WARN_ON(lockdep_is_held(&ar->conf_mutex));
 	/* make sure rcu-protected mac80211 tx path itself is drained */
 	synchronize_net();