Fix urcu-call-rcu-impl.h: false-sharing

Fix urcu-call-rcu-impl.h: false-sharing

> >  struct call_rcu_data {
> > -   struct cds_wfq_queue cbs;
> > +   /*
> > +    * Align the tail on cache line size to eliminate false-sharing
> > +    * with head.
> > +    */
> > +   struct cds_wfcq_tail __attribute__((aligned(CAA_CACHE_LINE_SIZE))) cbs_tail;
> > +   /* Alignment on cache line size will add padding here */
> > +
> > +   struct cds_wfcq_head cbs_head;
>
>
> wrong here. In this code, cbs_tail and cbs_head are in the same cache line.

Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>