Make CTransaction actually immutable

src/net_processing.cpp

@@ -1594,8 +1594,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
         deque<COutPoint> vWorkQueue;
         vector<uint256> vEraseQueue;
-        CTransaction tx;
-        vRecv >> tx;
+        CTransaction tx(deserialize, vRecv);
 
         CInv inv(MSG_TX, tx.GetHash());
         pfrom->AddInventoryKnown(inv);