net/bridge: Replace call_rcu_bh() and rcu_barrier_bh()

Now that call_rcu()'s callback is not invoked until after all bh-disable
regions of code have completed (in addition to explicitly marked
RCU read-side critical sections), call_rcu() can be used in place
of call_rcu_bh().  Similarly, rcu_barrier() can be used in place of
rcu_barrier_bh().  This commit therefore makes these changes.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Roopa Prabhu <roopa@cumulusnetworks.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: <bridge@lists.linux-foundation.org>
Cc: <netdev@vger.kernel.org>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>