Rebalance checkConnected()

Rebalance checkConnected()

AtomicBoolean forces the enclosed boolean to be cache-aligned,
needlessly hitting a cacheline. Since we only flip state only once,
when the connection is severed, we can turn this into a volatile
boolean.

Doing that is costing us a synchronized close(), but that is perfectly
acceptable, as that is called only once.

Change-Id: I76fda3d3f65a5f800e7d3970b0b8fe99fb3e8b6d
Signed-off-by: Robert Varga <nite@hq.sk>