netfilter: bridge: Don't sabotage nf_hook calls for an l3mdev slave

Followup to a173f066 ("netfilter: bridge: Don't sabotage nf_hook
calls from an l3mdev"). Some packets (e.g., ndisc) do not have the skb
device flipped to the l3mdev (e.g., VRF) device. Update ip_sabotage_in
to not drop packets for slave devices too. Currently, neighbor
solicitation packets for 'dev -> bridge (addr) -> vrf' setups are getting
dropped. This patch enables IPv6 communications for bridges with an
address that are enslaved to a VRF.

Fixes: 73e20b76 ("net: vrf: Add support for PREROUTING rules on vrf device")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/bridge/br_netfilter_hooks.c

@@ -831,7 +831,8 @@ static unsigned int ip_sabotage_in(void *priv,
 	struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
 
 	if (nf_bridge && !nf_bridge->in_prerouting &&
-	    !netif_is_l3_master(skb->dev)) {
+	    !netif_is_l3_master(skb->dev) &&
+	    !netif_is_l3_slave(skb->dev)) {
 		state->okfn(state->net, state->sk, skb);
 		return NF_STOLEN;
 	}