minimal send ack interval

libi2pd/Streaming.cpp

@@ -182,6 +182,7 @@ namespace stream
 					m_IsAckSendScheduled = true;
 					auto ackTimeout = m_RTT/10;
 					if (ackTimeout > m_AckDelay) ackTimeout = m_AckDelay;
+					else if (ackTimeout < MIN_SEND_ACK_TIMEOUT) ackTimeout = MIN_SEND_ACK_TIMEOUT;
 					m_AckSendTimer.expires_from_now (boost::posix_time::milliseconds(ackTimeout));
 					m_AckSendTimer.async_wait (std::bind (&Stream::HandleAckSendTimer,
 						shared_from_this (), std::placeholders::_1));

libi2pd/Streaming.h

@@ -58,6 +58,7 @@ namespace stream
 	const int MAX_WINDOW_SIZE = 128;
 	const int INITIAL_RTT = 8000; // in milliseconds
 	const int INITIAL_RTO = 9000; // in milliseconds
+	const int MIN_SEND_ACK_TIMEOUT = 2; // in milliseconds
 	const int SYN_TIMEOUT = 200; // how long we wait for SYN after follow-on, in milliseconds
 	const size_t MAX_PENDING_INCOMING_BACKLOG = 128;
 	const int PENDING_INCOMING_TIMEOUT = 10; // in seconds