Notify backchannel client of closed connection
Notify backchannel client of closed connection

Summary:
On Thrift server side, a callback passed to
getDuplexClient<Client>.getChannel().setCloseCallback() was not
executed when the Thrift client (the remote side) dropped the
connection. This diff fixes that.

Reviewed By: alandau

Differential Revision: D3534470

fbshipit-source-id: b96a3100dccdf79f74054dcd13c7b208320089f0

facebook/fbthrift,facebook/fbthrift,getyourguide/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,facebook/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,facebook/fbthrift,LinusU/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,facebook/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,facebook/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift