disconnect established session if clock skew detected

libi2pd/NTCP2.cpp

@@ -884,8 +884,20 @@ namespace transport
 			switch (blk)
 			{
 				case eNTCP2BlkDateTime:
+				{	
 					LogPrint (eLogDebug, "NTCP2: Datetime");
-				break;
+					if (m_IsEstablished)
+					{
+						uint64_t ts = i2p::util::GetSecondsSinceEpoch ();
+						uint64_t tsA = bufbe32toh (frame + offset);
+						if (tsA < ts - NTCP2_CLOCK_SKEW || tsA > ts + NTCP2_CLOCK_SKEW)
+						{
+							LogPrint (eLogWarning, "NTCP2: Established session time difference ", (int)(ts - tsA), " exceeds clock skew");
+							SendTerminationAndTerminate (eNTCP2ClockSkew);
+						}	
+					}		
+					break;
+				}
 				case eNTCP2BlkOptions:
 					LogPrint (eLogDebug, "NTCP2: Options");
 				break;

libi2pd/SSU2Session.cpp

@@ -1617,6 +1617,7 @@ namespace transport
 		{
 			case eSSU2SessionStateSessionRequestReceived:
 			case eSSU2SessionStateTokenRequestReceived:
+			case eSSU2SessionStateEstablished:	
 				if (std::abs (offset) > SSU2_CLOCK_SKEW)
 					m_TerminationReason = eSSU2TerminationReasonClockSkew;
 			break;