multi: make sure CPFP won't exceed max allowed fee rate

This commit updates the `fee()` method in `weightEstimator` to make sure
when doing CPFP we are not exceeding the max allowed fee rate. In order
to use the max fee rate, we need to modify several methods to pass the
configured value to the estimator.

itest/lnd_onchain_test.go

@@ -229,9 +229,12 @@ func runCPFP(ht *lntest.HarnessTest, alice, bob *node.HarnessNode) {
 
 	// We'll attempt to bump the fee of this transaction by performing a
 	// CPFP from Alice's point of view.
+	maxFeeRate := uint64(sweep.DefaultMaxFeeRate)
 	bumpFeeReq := &walletrpc.BumpFeeRequest{
-		Outpoint:    op,
-		SatPerVbyte: uint64(sweep.DefaultMaxFeeRate),
+		Outpoint: op,
+		// We use a higher fee rate than the default max and expect the
+		// sweeper to cap the fee rate at the max value.
+		SatPerVbyte: maxFeeRate * 2,
 	}
 	bob.RPC.BumpFee(bumpFeeReq)
 
@@ -249,8 +252,11 @@ func runCPFP(ht *lntest.HarnessTest, alice, bob *node.HarnessNode) {
 		"output txid not matched")
 	require.Equal(ht, pendingSweep.Outpoint.OutputIndex, op.OutputIndex,
 		"output index not matched")
-	require.Equal(ht, pendingSweep.SatPerVbyte, bumpFeeReq.SatPerVbyte,
-		"sweep sat per vbyte not matched")
+
+	// Also validate that the fee rate is capped at the max value.
+	require.Equalf(ht, maxFeeRate, pendingSweep.SatPerVbyte,
+		"sweep sat per vbyte not matched, want %v, got %v",
+		maxFeeRate, pendingSweep.SatPerVbyte)
 
 	// Mine a block to clean up the unconfirmed transactions.
 	ht.MineBlocksAndAssertNumTxes(1, 2)