Fix for wrong auto rotation on iOS

iOS has inverted LanscapeLeft and LandscapeRight orientation compared to XNA.
While other methods take that in account, it was missing in ToUIInterfaceOrientationMask, which was a potential source of unwanted auto rotation and crashes if the rotation resulted in unsupported Info.plist orientations.

See codeplex discussion for details: https://monogame.codeplex.com/discussions/535677