Add support for tx-relay via wtxid

This adds a field to CNodeState that tracks whether to relay transactions with
that peer via wtxid, instead of txid. As of this commit the field will always
be false, but in a later commit we will add a way to negotiate turning this on
via p2p messages exchanged with the peer.

src/node/transaction.cpp

@@ -78,7 +78,8 @@ TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef t
     }
 
     if (relay) {
-        RelayTransaction(hashTx, *node.connman);
+        LOCK(cs_main);
+        RelayTransaction(hashTx, tx->GetWitnessHash(), *node.connman);
     }
 
     return TransactionError::OK;