staging: lustre: llite: add xattr.h header to xattr.c

staging: lustre: llite: add xattr.h header to xattr.c

The reason xattr.c can compile without xattr.h is due
to lustre_compact.h being included. That header will
eventually go away so lets directly include xattr.h.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-7244
Reviewed-on: http://review.whamcloud.com/16707
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>