Currently direct_fd_ping runs without timeout, but the verb is not
waited forever, the wait is canceled after a timeout, this timeout
simply is not passed to the rpc. It may create a situation where the
rpc callback can runs on a destination but it is no longer waited on.
Change the code to pass timeout to rpc as well and return earlier from
the rpc handler if the timeout is reached by the time the callback is
called. This is backwards compatible since timeout is passed as
optional.
82f80478b8