limit received SSU2 packets queue

libi2pd/SSU2.h

@@ -37,6 +37,7 @@ namespace transport
 	const uint64_t SSU2_SOCKET_MAX_BUFFER_SIZE = 4 * 1024 * 1024;
 	const size_t SSU2_MAX_NUM_INTRODUCERS = 3;
 	const size_t SSU2_MIN_RECEIVED_PACKET_SIZE = 40; // 16 byte short header + 8 byte minimum payload + 16 byte MAC
+	const size_t SSU2_MAX_RECEIVED_QUEUE_SIZE = 2500; // in packets
 	const int SSU2_TO_INTRODUCER_SESSION_DURATION = 3600; // 1 hour
 	const int SSU2_TO_INTRODUCER_SESSION_EXPIRATION = 4800; // 80 minutes
 	const int SSU2_KEEP_ALIVE_INTERVAL = 15; // in seconds