multi: new bitcoind rpcpolling backend for itests

lntest/bitcoind.go

@@ -1,5 +1,5 @@
-//go:build bitcoind && !notxindex
-// +build bitcoind,!notxindex
+//go:build bitcoind && !notxindex && !rpcpolling
+// +build bitcoind,!notxindex,!rpcpolling
 
 package lntest
 
@@ -19,5 +19,5 @@ func NewBackend(miner string, netParams *chaincfg.Params) (
 		"-disablewallet",
 	}
 
-	return newBackend(miner, netParams, extraArgs)
+	return newBackend(miner, netParams, extraArgs, false)
 }