title: Game Center Multiplayer using GKMatch but seems can't be connected
body: <p>Hi I'm a new bie in Game Center for iOS.  I'm trying to add the multiplayer feature using matches to my game and following the documentation.</p>
  
  <p>So far I reached a point where 2 of my clients can successfully get a match, i.e. the matchmakerViewController:didFindMatch callback is called and a GKMatch object is delivered.</p>
  
  <p>However after that I seems to be stuck there forever, because according to the documentation,  I'll have to wait until all the players (2 in my case) are actually connected before starting my game.   But it seems the match:player:didChangeState callback is never called to indicate a successful connection.   Well, I'm sure my clients are all in the same wifi network ( or is it a must?)  Could any one enlighten me on this case?  Do I have to do any extra things to make the clients to connect?    Thanks a lot for the help!</p>