Do multicast interface selection portably for router advertisements.

src/radv.c

@@ -391,10 +391,13 @@ static void send_ra(time_t now, int iface, char *iface_name, struct in6_addr *de
 	addr.sin6_scope_id = iface;
     }
   else
-    inet_pton(AF_INET6, ALL_NODES, &addr.sin6_addr); 
+    {
+      inet_pton(AF_INET6, ALL_NODES, &addr.sin6_addr); 
+      setsockopt(daemon->icmp6fd, IPPROTO_IPV6, IPV6_MULTICAST_IF, &iface, sizeof(iface));
+    }
   
-  send_from(daemon->icmp6fd, 0, daemon->outpacket.iov_base, save_counter(0),
-	    (union mysockaddr *)&addr, (struct all_addr *)&parm.link_local, iface); 
+  while (sendto(daemon->icmp6fd, daemon->outpacket.iov_base, save_counter(0), 0, 
+		(struct sockaddr *)&addr, sizeof(addr)) == -1 && retry_send());
   
 }