refactor: add GenTxid (=txid or wtxid) type and use it for tx request logic

src/protocol.cpp

@@ -241,3 +241,9 @@ std::vector<std::string> serviceFlagsToStr(uint64_t flags)
 
     return str_flags;
 }
+
+GenTxid ToGenTxid(const CInv& inv)
+{
+    assert(inv.IsGenTxMsg());
+    return {inv.IsMsgWtx(), inv.hash};
+}