Multicast forwarding is separated from the routing flag

Previously Multicast was always forwarded by default.
But as multicast forwarding and default routing are separate the
multicast forward was not enabled if the Border router was not
main border router all the time.

source/6LoWPAN/Thread/thread_bbr_api.c

@@ -629,13 +629,14 @@ static void thread_bbr_network_data_send(thread_bbr_t *this, uint8_t prefix[8],
 
 static void thread_bbr_routing_enable(thread_bbr_t *this, bool multicast_routing_enabled)
 {
+    // Start multicast proxying
+    // We do not enable multicast forwarding as there is other default router present in network
+    multicast_fwd_set_forwarding(this->interface_id, multicast_routing_enabled);
+
     if (this->routing_enabled) {
         return;
     }
     tr_info("br: enable routing");
-    // Start multicast proxying
-    // We do not enable multicast forwarding as there is other default router present in network
-    multicast_fwd_set_forwarding(this->interface_id, multicast_routing_enabled);
     this->routing_enabled = true;
 }