AsyncUDPSocket: fixing documentation

Summary: in D13274704 default has been changed to OFF. fixing comment

Reviewed By: yfeldblum

Differential Revision: D13590584

fbshipit-source-id: af1bac2b866aa55f9645ce33da6e8850cd136d31

folly/io/async/AsyncUDPSocket.h

@@ -212,7 +212,7 @@ class AsyncUDPSocket : public EventHandler {
   }
 
   /**
-   * Set SO_REUSEADDR flag on the socket. Default is ON.
+   * Set SO_REUSEADDR flag on the socket. Default is OFF.
    */
   virtual void setReuseAddr(bool reuseAddr) {
     reuseAddr_ = reuseAddr;