Some fields in "struct net_bridge" aren't available when compiling the
kernel without IPv6 support. Therefore adding a check/macro to skip the
complaining code sections in that case.
Introduced by 
2cd4143192e8c60f66cb32c3a30c76d0470a372d
("bridge: memorize and export selected IGMP/MLD querier port")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
 
                    rcu_dereference(br->ip4_querier.port) == port)
                        goto unlock;
                break;
+#if IS_ENABLED(CONFIG_IPV6)
        case ETH_P_IPV6:
                if (!timer_pending(&br->ip6_other_query.timer) ||
                    rcu_dereference(br->ip6_querier.port) == port)
                        goto unlock;
                break;
+#endif
        default:
                goto unlock;
        }