uClibc systems dont define IPV6_V6ONLY when USE=-ipv6

--- avahi-core/socket.c
+++ avahi-core/socket.c
@@ -360,6 +360,7 @@
 }
 
 int avahi_open_socket_ipv6(int no_reuse) {
+#ifdef IPV6_V6ONLY
     struct sockaddr_in6 sa, local;
     int fd = -1, yes, r;
     int ttl;
@@ -425,6 +426,7 @@
 fail:
     if (fd >= 0)
         close(fd);
+#endif
 
     return -1;
 }