Fix ipv6 connection hangs when in v4 environment

[ayanamist]

Since connection will be reset to USE_IPV4_IPV6_RANDOM when connection failed even in pure v4 environment.

Telegram/TMessagesProj/jni/tgnet/Connection.cpp

Lines 699 to 702 in 0e17caa

	if (currentDatacenter->isRepeatCheckingAddresses() && (ConnectionsManager::getInstance(currentDatacenter->instanceNum).getIpStratagy() == USE_IPV4_ONLY || ConnectionsManager::getInstance(currentDatacenter->instanceNum).getIpStratagy() == USE_IPV6_ONLY)) {
	if (LOGS_ENABLED) DEBUG_D("started retrying connection, set ipv4 ipv6 random strategy");
	ConnectionsManager::getInstance(currentDatacenter->instanceNum).setIpStrategy(USE_IPV4_IPV6_RANDOM);
	}

However, it does not reset lastProtocolUsefullData correctly if connectionType is not ConnectionTypeGeneric (usually problem occurs when ConnectionTypeGenericMedia) and lastProtocolUsefullData will be set false only here.

Telegram/TMessagesProj/jni/tgnet/Connection.cpp

Lines 299 to 311 in 0e17caa

	} else if (strategy == USE_IPV4_IPV6_RANDOM) {
	if (ConnectionsManager::getInstance(currentDatacenter->instanceNum).lastProtocolUsefullData) {
	ipv6 = ConnectionsManager::getInstance(currentDatacenter->instanceNum).lastProtocolIsIpv6 ? TcpAddressFlagIpv6 : 0;
	} else {
	uint8_t value;
	RAND_bytes(&value, 1);
	ipv6 = value % 3 == 0 ? TcpAddressFlagIpv6 : 0;
	ConnectionsManager::getInstance(currentDatacenter->instanceNum).lastProtocolIsIpv6 = ipv6 != 0;
	}
	if (connectionType == ConnectionTypeGeneric) {
	ConnectionsManager::getInstance(currentDatacenter->instanceNum).lastProtocolUsefullData = false;
	}
	} else {

So it always connect as ipv6 if lastProtocolUsefullData is true and RAND_bytes got 0, 3, 6 even there is no ipv6 capability.

I try to fix it using always reset lastProtocolUsefullData to false when USE_IPV4_IPV6_RANDOM is meet.