bridge: Use RCU list primitive in __br_mdb_ip_get

As Paul McKenney correctly pointed out, __br_mdb_ip_get needs
to use the RCU list walking primitive in order to work correctly
on platforms where data-dependency ordering is not guaranteed.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_multicast.c

@@ -38,7 +38,7 @@ static struct net_bridge_mdb_entry *__br_mdb_ip_get(
 	struct net_bridge_mdb_entry *mp;
 	struct hlist_node *p;
 
-	hlist_for_each_entry(mp, p, &mdb->mhash[hash], hlist[mdb->ver]) {
+	hlist_for_each_entry_rcu(mp, p, &mdb->mhash[hash], hlist[mdb->ver]) {
 		if (dst == mp->addr)
 			return mp;
 	}