Revert "cameraview: remove glflush, reduce C3 CPU usage (#22949)"

This reverts commit 33b1b94067.

selfdrive/test/test_onroad.py

@@ -56,7 +56,7 @@ if TICI:
     "./loggerd": 70.0,
     "selfdrive.controls.controlsd": 28.0,
     "./camerad": 31.0,
-    "./_ui": 21.0,
+    "./_ui": 30.2,
     "selfdrive.controls.plannerd": 11.7,
     "./_dmonitoringmodeld": 10.0,
     "selfdrive.locationd.paramsd": 5.0,

selfdrive/ui/qt/widgets/cameraview.cc

@@ -307,6 +307,7 @@ void CameraViewWidget::vipcThread() {
 
         emit vipcThreadFrameReceived(buf);
 
+        glFlush();
       } else {
         emit vipcThreadFrameReceived(buf);
       }