LU-8907 llite: handle client racy case during create

LU-8907 llite: handle client racy case during create

Some very infrequent situations exists on client side
able to cause a race during create when concurrent access
by fid occurs. The result of the race can allow a d_alias
to be already present when it was not expected when original
code/LBUG has been written.

One of the identified scenario is when a concurrent access of
inode thru the .lustre/fid/<[FID]> method occurs.

New sanity/test_161d has been added to reproduce this scenario.

Final fix is to remove inaccurate
LASSERT(ll_d_hlist_empty(&inode->i_dentry));
in ll_create_node().

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I1ff19883cc5b53831f1d5c577f4152225fa9e0fb
Reviewed-on: https://review.whamcloud.com/25296
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>