Minimize conditional compilation in AsyncUDPSocket
Minimize conditional compilation in AsyncUDPSocket

Summary: [Folly] Minimize conditional compilation in `AsyncUDPSocket`.

Differential Revision: D23172282

fbshipit-source-id: 6ead5cf2232b9db0f709080666262ccc4b5984da

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly