This should fix #27726. With enough load, it might happen that the SetPongHandler 
callback gets invoked before the call to SetReadDeadline is made in pingLoop. When 
this occurs, the socket will end up with a 30s read deadline even though it got the pong,
which will lead to a timeout.

The fix here is processing the pong on pingLoop, synchronizing with the code that 
sends the ping.