mac80211: improve __rate_control_send_low warning

If there are no supported rates in the rate mask with the required
flags, we warn, but it's not clear which part causes the warning.

Add the relevant data to the warning to understand why it happens.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rate.c

@@ -305,7 +305,10 @@ static void __rate_control_send_low(struct ieee80211_hw *hw,
 		info->control.rates[0].idx = i;
 		break;
 	}
-	WARN_ON_ONCE(i == sband->n_bitrates);
+	WARN_ONCE(i == sband->n_bitrates,
+		  "no supported rates (0x%x) in rate_mask 0x%x with flags 0x%x\n",
+		  sta ? sta->supp_rates[sband->band] : 0,
+		  rate_mask, rate_flags);
 
 	info->control.rates[0].count =
 		(info->flags & IEEE80211_TX_CTL_NO_ACK) ?