Set desktop file name for QApplication

This must match the base name of the .desktop file (without the .desktop suffix).

The implicit default is 'wireshark', which worked until the file got renamed in 42a09ad02e

Setting this is important for several desktop enviromnent features to work, for example the window icon on Plasma Wayland

ui/qt/wireshark_application.cpp

@@ -663,6 +663,8 @@ WiresharkApplication::WiresharkApplication(int &argc,  char **argv) :
     styleHints()->setShowShortcutsInContextMenus(true);
 #endif
 
+    setDesktopFileName(QStringLiteral("org.wireshark.Wireshark"));
+
     //
     // XXX - this means we try to check for the existence of all files
     // in the recent list every 2 seconds; that causes noticeable network