sweep: update getInputWitnessSizeUpperBound to be aware of nested p2sh

In this commit, we update the `getInputWitnessSizeUpperBound` and all
its callers to be aware of nested p2sh witness inputs. We do so by
adding another bool which is true if the output is a nested p2sh output.
If so, then in order to properly estimate the total weight, the caller
needs to factor in the non-witness data of the additional sigScript data
push.

sweep/sweeper_test.go

@@ -10,6 +10,7 @@ import (
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/build"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lnwallet"
@@ -376,7 +377,8 @@ func TestNegativeInput(t *testing.T) {
 	if !testTxIns(&sweepTx1, []*wire.OutPoint{
 		largeInput.OutPoint(), positiveInput.OutPoint(),
 	}) {
-		t.Fatal("Tx does not contain expected inputs")
+		t.Fatalf("Tx does not contain expected inputs: %v",
+			spew.Sdump(sweepTx1))
 	}
 
 	ctx.backend.mine()