Replace calls to GetHash() with GetTxid() for transaction objects.

Where the caller intends to receive a transaction id and not a double
SHA256 hash.

src/net.cpp

@@ -1751,7 +1751,7 @@ void RelayTransaction(const CTransaction& tx)
 
 void RelayTransaction(const CTransaction& tx, const CDataStream& ss)
 {
-    CInv inv(MSG_TX, tx.GetHash());
+    CInv inv(MSG_TX, tx.GetTxid());
     {
         LOCK(cs_mapRelay);
         // Expire old relay messages