Make debug print clearer for AP/mesh mode secondary channel issues

If the secondary channel was not found at all, no debug print was shown
to indicate that the channel was rejected due to that problem. Print a
clearer message indicating which channel was behind the reason to reject
channel configuration as unsuitable for AP mode.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/ap/hw_features.c

@@ -785,6 +785,8 @@ static int hostapd_is_usable_chan(struct hostapd_iface *iface,
 			   chan->flag & HOSTAPD_CHAN_RADAR ? " RADAR" : "");
 	}
 
+	wpa_printf(MSG_INFO, "Channel %d (%s) not allowed for AP mode",
+		   channel, primary ? "primary" : "secondary");
 	return 0;
 }