[Qt] Change RBF checkbox to reflect -walletrbf setting

Before this commit, the checkbox would always start off unchecked. After this
commit it will respect the -walletrbf setting (which is currently false by
default).

src/qt/sendcoinsdialog.cpp

@@ -112,6 +112,7 @@ SendCoinsDialog::SendCoinsDialog(const PlatformStyle *_platformStyle, QWidget *p
     ui->groupCustomFee->button((int)std::max(0, std::min(1, settings.value("nCustomFeeRadio").toInt())))->setChecked(true);
     ui->customFee->setValue(settings.value("nTransactionFee").toLongLong());
     ui->checkBoxMinimumFee->setChecked(settings.value("fPayOnlyMinFee").toBool());
+    ui->optInRBF->setCheckState(model->getDefaultWalletRbf() ? Qt::Checked : Qt::Unchecked);
     minimizeFeeSection(settings.value("fFeeSectionMinimized").toBool());
 }
 

src/qt/walletmodel.cpp

@@ -706,3 +706,8 @@ int WalletModel::getDefaultConfirmTarget() const
 {
     return nTxConfirmTarget;
 }
+
+bool WalletModel::getDefaultWalletRbf() const
+{
+    return fWalletRbf;
+}

src/qt/walletmodel.h

@@ -213,6 +213,8 @@ public:
 
     int getDefaultConfirmTarget() const;
 
+    bool getDefaultWalletRbf() const;
+
 private:
     CWallet *wallet;
     bool fHaveWatchOnly;