quectel: Extend power-on timeout

More complicated modems emerge and they need longer start-up times. An
EC21 takes about 13 seconds to boot up. This is slightly longer than the
20 * 500 ms we have at the moment. This extends the retries to 30, so we
have 30 * 500 ms and this does successfully power up an EC21 modem.

plugins/quectel.c

@@ -1086,8 +1086,8 @@ static void init_timeout_cb(struct l_timeout *timeout, void *user_data)
 
 	DBG("%p", modem);
 
-	if (data->init_count++ >= 20) {
-		ofono_error("failed to init modem after 20 attempts");
+	if (data->init_count++ >= 30) {
+		ofono_error("failed to init modem after 30 attempts");
 		close_serial(modem);
 		return;
 	}