CameraServer: Workaround LabVIEW dashboard OpenCV compatibility. (#406)

The current LabVIEW dashboard (Beta 4) requires the source type to be either
"usb:" or "ip:" and does not support "cv:".  To work around this, use a source
type of "usb:" for OpenCV sources as well.

Workaround for #407.

wpilibc/athena/src/CameraServer.cpp

@@ -38,7 +38,9 @@ static llvm::StringRef MakeSourceValue(CS_Source source,
       break;
     }
     case cs::VideoSource::kCv:
-      return "cv:";
+      // FIXME: Should be "cv:", but LabVIEW dashboard requires "usb:".
+      // https://github.com/wpilibsuite/allwpilib/issues/407
+      return "usb:";
     default:
       return "unknown:";
   }