If the task->tk_exit() wants to restart the RPC call after delaying
then the current RPC code will clobber the timer by calling
rpc_delete_timer() immediately after re-entering the loop in
__rpc_execute().
Problem noticed by Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>