LU-6215 llite: filldir_t api changed for 3.18 kernels

LU-6215 llite: filldir_t api changed for 3.18 kernels

The filldir_t callback went from passing in a void *cookie
to struct dir_context instead. Here we enable handling this
api change in newer kernels. This functionality is used for
nfs over lustre support.

Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Change-Id: I5de025306ace61b8defdce227fe12b854caf1b3b
Reviewed-on: http://review.whamcloud.com/14681
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>