staging: lustre: use wait_event_idle_timeout in ptlrpcd()

We can replace l_wait_event() with
wait_event_idle_timeout() here providing we call the
timeout function when wait_event_idle_timeout() returns zero.

As ptlrpc_expired_set() returns 1, the l_wait_event() aborts of the
first timeout.

Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>