LU-4416 osd-ldiskfs: set I_LINKABLE for inc_nlink

LU-4416 osd-ldiskfs: set I_LINKABLE for inc_nlink

Linux commit f4e0c30c191 (allow the temp files created by open() to be
linked to) put in a check to warn if I_LINKABLE was not set
when trying to pull nlinks up from 0. This patch sets the flag
to properly allow it.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I2a71d0515f3735f8eb3e94d190e68e41a36e0f68
Reviewed-on: http://review.whamcloud.com/10375
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>