net: ip: mld: Ensure MLD APIs work with offloaded interfaces

MLD APIs are commonly used across the codebase to configure IPv6
multicast addresses on network interfaces. Sending MLD reports however
works only for native interfaces as it uses low-level APIs. Therefore,
in order to make the APIs at least semi-functional for offloaded
interfaces as well (i.e. allow to configure multicast address on
the interface), return early in case interface is offloaded.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

Author: rlubos

subsys/net/ip/ipv6_mld.c

@@ -213,7 +213,7 @@ int net_ipv6_mld_send_single(struct net_if *iface, const struct in6_addr *addr,
 int net_ipv6_mld_join(struct net_if *iface, const struct in6_addr *addr)
 {
 	struct net_if_mcast_addr *maddr;
-	int ret;
+	int ret = 0;
 
 	maddr = net_if_ipv6_maddr_lookup(addr, &iface);
 	if (maddr && net_if_ipv6_maddr_is_joined(maddr)) {
@@ -235,11 +235,16 @@ int net_ipv6_mld_join(struct net_if *iface, const struct in6_addr *addr)
 		return -ENETDOWN;
 	}
 
+	if (net_if_is_offloaded(iface)) {
+		goto out;
+	}
+
 	ret = net_ipv6_mld_send_single(iface, addr, NET_IPV6_MLDv2_CHANGE_TO_EXCLUDE_MODE);
 	if (ret < 0) {
 		return ret;
 	}
 
+out:
 	net_if_ipv6_maddr_join(iface, maddr);
 
 	net_if_mcast_monitor(iface, &maddr->address, true);
@@ -254,7 +259,7 @@ int net_ipv6_mld_join(struct net_if *iface, const struct in6_addr *addr)
 int net_ipv6_mld_leave(struct net_if *iface, const struct in6_addr *addr)
 {
 	struct net_if_mcast_addr *maddr;
-	int ret;
+	int ret = 0;
 
 	maddr = net_if_ipv6_maddr_lookup(addr, &iface);
 	if (!maddr) {
@@ -269,11 +274,16 @@ int net_ipv6_mld_leave(struct net_if *iface, const struct in6_addr *addr)
 		return 0;
 	}
 
+	if (net_if_is_offloaded(iface)) {
+		goto out;
+	}
+
 	ret = net_ipv6_mld_send_single(iface, addr, NET_IPV6_MLDv2_CHANGE_TO_INCLUDE_MODE);
 	if (ret < 0) {
 		return ret;
 	}
 
+out:
 	net_if_mcast_monitor(iface, &maddr->address, false);
 
 	net_mgmt_event_notify_with_info(NET_EVENT_IPV6_MCAST_LEAVE, iface,