p2p: Don't use timestamps from inbound peers

This makes it harder for others to tamper with
our adjusted time.

Author: mzumsande

src/net_processing.cpp

@@ -2683,7 +2683,11 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
 
         int64_t nTimeOffset = nTime - GetTime();
         pfrom.nTimeOffset = nTimeOffset;
-        AddTimeData(pfrom.addr, nTimeOffset);
+        if (!pfrom.IsInboundConn()) {
+            // Don't use timedata samples from inbound peers to make it
+            // harder for others to tamper with our adjusted time.
+            AddTimeData(pfrom.addr, nTimeOffset);
+        }
 
         // If the peer is old enough to have the old alert system, send it the final alert.
         if (greatest_common_version <= 70012) {