[net processing] Rename nStartingHeight to m_starting_height

Not done as a scripted diff to avoid misnaming the local variable in
ProcessMessage().

src/qt/rpcconsole.cpp

@@ -1135,7 +1135,7 @@ void RPCConsole::updateDetailWidget()
         else
             ui->peerCommonHeight->setText(tr("Unknown"));
 
-        ui->peerHeight->setText(QString::number(stats->nodeStateStats.nStartingHeight));
+        ui->peerHeight->setText(QString::number(stats->nodeStateStats.m_starting_height));
     }
 
     ui->detailWidget->show();