Format IPv4 updates better.

message.c

@@ -219,7 +219,7 @@ parse_packet(const unsigned char *from, struct network *net,
                 unsigned char p4[16], prefix[16], nh[16];
                 v4tov6(p4, message + 20);
                 v4tov6(nh, message + 16);
-                debugf("Received IPv4 prefix %s nh %s on %s from %s (%s).\n",
+                debugf("Received update for %s nh %s on %s from %s (%s).\n",
                        format_prefix(p4, plen),
                        format_address(nh),
                        net->ifname,