bridge: vlan: Use rcu_dereference instead of rtnl_dereference

br_should_learn() is protected by RCU and not by RTNL, so use correct
flavor of nbp_vlan_group().

Fixes: 907b1e6e83ed ("bridge: vlan: use proper rcu for the vlgrp
member")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_vlan.c

@@ -482,7 +482,7 @@ bool br_should_learn(struct net_bridge_port *p, struct sk_buff *skb, u16 *vid)
 	if (!br->vlan_enabled)
 		return true;
 
-	vg = nbp_vlan_group(p);
+	vg = nbp_vlan_group_rcu(p);
 	if (!vg || !vg->num_vlans)
 		return false;