staging/lustre/llite: ASSERTION( atomic_read(&d->ld_ref) == 0 ) failed

ll_iget_for_nfs() can call unbalanced iput() causing memory
leaks. This patch removes this iput() call.

Also, avoid unhashing disconnected dentries in
d_lustre_invalidate(), which is another source of memory
leaks.

One of the symptoms of the leak is the following crash pattern:
LustreError: 14812:0:(lu_object.c:1251:lu_device_fini())
 ASSERTION( atomic_read(&d->ld_ref) == 0 ) failed: Refcount is 1
LustreError: 14812:0:(lu_object.c:1251:lu_device_fini()) LBUG
Pid: 14812, comm: umount

Call Trace:
 [<ffffffffa11bc895>] libcfs_debug_dumpstack+0x55/0x80 [libcfs]
 [<ffffffffa11bce97>] lbug_with_loc+0x47/0xb0 [libcfs]
 [<ffffffffa1458a48>] lu_device_fini+0xb8/0xc0 [obdclass]
 [<ffffffffa08e9ab2>] lovsub_device_free+0x52/0x220 [lov]
 [<ffffffffa145c64e>] lu_stack_fini+0x7e/0xc0 [obdclass]
 [<ffffffffa146356e>] cl_stack_fini+0xe/0x10 [obdclass]
 [<ffffffffa08bc1a8>] lov_device_fini+0x58/0x120 [lov]
 [<ffffffffa145c619>] lu_stack_fini+0x49/0xc0 [obdclass]
 [<ffffffffa146356e>] cl_stack_fini+0xe/0x10 [obdclass]
 [<ffffffffa0e1279d>] cl_sb_fini+0x6d/0x190 [lustre]
 [<ffffffffa0dd34bc>] ll_put_super+0x1bc/0x11e0 [lustre]
 [<ffffffff811cd0f2>] ? fsnotify_clear_marks_by_inode+0x32/0xf0
 [<ffffffff811a59df>] ? destroy_inode+0x2f/0x60
 [<ffffffff811a5eac>] ? dispose_list+0xfc/0x120
 [<ffffffff811a62a6>] ? invalidate_inodes+0xf6/0x190
 [<ffffffff8118b35b>] generic_shutdown_super+0x5b/0xe0
 [<ffffffff8118b446>] kill_anon_super+0x16/0x60
 [<ffffffffa144e7ba>] lustre_kill_super+0x4a/0x60 [obdclass]
 [<ffffffff8118bbe7>] deactivate_super+0x57/0x80
 [<ffffffff811aabef>] mntput_no_expire+0xbf/0x110
 [<ffffffff811ab73b>] sys_umount+0x7b/0x3a0
 [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b

Signed-off-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Reviewed-on: http://review.whamcloud.com/15480
Xyratex-bug-id: MRP-2414
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6794


Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>