DolphinQt2/NetPlay: Mark constructors explicit where applicable

Source/Core/DolphinQt2/NetPlay/MD5Dialog.h

@@ -17,7 +17,7 @@ class MD5Dialog : public QDialog
 {
   Q_OBJECT
 public:
-  MD5Dialog(QWidget* parent);
+  explicit MD5Dialog(QWidget* parent);
 
   void show(const QString& title);
   void SetProgress(int pid, int progress);

Source/Core/DolphinQt2/NetPlay/NetPlayDialog.h

@@ -30,7 +30,7 @@ class NetPlayDialog : public QDialog, public NetPlayUI
 {
   Q_OBJECT
 public:
-  NetPlayDialog(QWidget* parent);
+  explicit NetPlayDialog(QWidget* parent);
   ~NetPlayDialog();
 
   void show(std::string nickname, bool use_traversal);

Source/Core/DolphinQt2/NetPlay/NetPlaySetupDialog.h

@@ -22,7 +22,7 @@ class NetPlaySetupDialog : public QDialog
 {
   Q_OBJECT
 public:
-  NetPlaySetupDialog(QWidget* parent);
+  explicit NetPlaySetupDialog(QWidget* parent);
 
   void accept() override;
   void show();