fix grouping for isActive - socket.isBound is almost always true

This change restores firing the channel's inactive event. That event is meant to fire when the channel transitions from active to not active, but from the [JDK documentation for DatagramSockets for 'isBound'](http://download.java.net/jdk7/archive/b123/docs/api/java/net/DatagramSocket.html#isBound()):
>Returns the binding state of the socket.
>If the socket was bound prior to being closed, then this method will continue to return true after the socket is closed.

So, once bound, the channel is always active - even if it's been closed and/or disconnected. The `|| socket.isBound()` was overriding the first part of that expression. Added some parentheses to fix grouping in the boolean expression.