nl80211: Make sure scan frequency debug buffer is NUL terminated

In theory, os_snprintf() could have filled the buffer to the end and
while the pos variable would not have been incremented beyond that,
there would not necessarily be a NUL termination at the end. Force the
array to end in NUL just in case.

Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>

src/drivers/driver_nl80211_event.c

@@ -1737,6 +1737,7 @@ static void send_scan_event(struct wpa_driver_nl80211_data *drv, int aborted,
 		}
 		info->freqs = freqs;
 		info->num_freqs = num_freqs;
+		msg[sizeof(msg) - 1] = '\0';
 		wpa_printf(MSG_DEBUG, "nl80211: Scan included frequencies:%s",
 			   msg);
 	}