Convert CompareInvMempoolOrder to GenTxidVariant

Now that we are storing `CTxMemPool::CompareDepthAndScore` parameters using
`std::variant` we have no portable zero-overhead way of accessing them,
so use `std::visit` and drop `bool wtxid` in-parameter.

Co-authored-by: stickies-v <stickies-v@protonmail.com>

src/net_processing.h

@@ -119,7 +119,7 @@ public:
     virtual PeerManagerInfo GetInfo() const = 0;
 
     /** Relay transaction to all peers. */
-    virtual void RelayTransaction(const uint256& txid, const uint256& wtxid) = 0;
+    virtual void RelayTransaction(const Txid& txid, const Wtxid& wtxid) = 0;
 
     /** Send ping message to all peers */
     virtual void SendPings() = 0;