Introduce a type of hlist that can support the use of the lowest bit in the
hlist_head. This will be subsequently used to implement per-bucket bit spinlock
for inode and dentry hashes, and may be useful in other cases such as network
hashes.
Reviewed-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NNick Piggin <npiggin@kernel.dk>