The RCU docs used to state that rcu_barrier() included a wait
for an RCU grace period; however the comments for rcu_barrier()
as of commit f0a0e6f2... "rcu: Clarify memory-ordering properties
of grace-period primitives" contradict this.

So add back synchronize_{rcu,net}() to where they once were,
but keep the rcu_barrier()s for the call_rcu() callbacks.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: NBob Copeland <bob@cozybit.com>
Reviewed-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>