Make fDisconnect an std::atomic

src/net.h

@@ -630,7 +630,7 @@ public:
     const bool fInbound;
     bool fNetworkNode;
     bool fSuccessfullyConnected;
-    bool fDisconnect;
+    std::atomic_bool fDisconnect;
     // We use fRelayTxes for two purposes -
     // a) it allows us to not relay tx invs before receiving the peer's version message
     // b) the peer may tell us in its version message that we should not relay tx invs