net: bridge: mcast: add wrappers for router node retrieval

In preparation for the upcoming split of multicast router state into
their IPv4 and IPv6 variants and to avoid IPv6 #ifdef clutter later add
two wrapper functions for router node retrieval in the payload
forwarding code.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_forward.c

@@ -276,7 +276,8 @@ void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 	bool allow_mode_include = true;
 	struct hlist_node *rp;
 
-	rp = rcu_dereference(hlist_first_rcu(&br->ip4_mc_router_list));
+	rp = br_multicast_get_first_rport_node(br, skb);
+
 	if (mdst) {
 		p = rcu_dereference(mdst->ports);
 		if (br_multicast_should_handle_mode(br, mdst->addr.proto) &&
@@ -290,7 +291,7 @@ void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 		struct net_bridge_port *port, *lport, *rport;
 
 		lport = p ? p->key.port : NULL;
-		rport = hlist_entry_safe(rp, struct net_bridge_port, ip4_rlist);
+		rport = br_multicast_rport_from_node_skb(rp, skb);
 
 		if ((unsigned long)lport > (unsigned long)rport) {
 			port = lport;

net/bridge/br_private.h

@@ -864,6 +864,16 @@ static inline bool br_group_is_l2(const struct br_ip *group)
 #define mlock_dereference(X, br) \
 	rcu_dereference_protected(X, lockdep_is_held(&br->multicast_lock))
 
+static inline struct hlist_node *
+br_multicast_get_first_rport_node(struct net_bridge *b, struct sk_buff *skb) {
+	return rcu_dereference(hlist_first_rcu(&b->ip4_mc_router_list));
+}
+
+static inline struct net_bridge_port *
+br_multicast_rport_from_node_skb(struct hlist_node *rp, struct sk_buff *skb) {
+	return hlist_entry_safe(rp, struct net_bridge_port, ip4_rlist);
+}
+
 static inline bool br_multicast_is_router(struct net_bridge *br)
 {
 	return br->multicast_router == 2 ||