rtadvd: use log_warnx when errno is not set

[Florian Obser]

OK?

diff --git if.c if.c
index 95f83d8e822..cc878bd5916 100644
--- if.c
+++ if.c
@@ -435,7 +435,7 @@ parse_iflist(struct if_msghdr ***ifmlist_p, char *buf, 
size_t bufsize)
        lim = buf + bufsize;
        for (ifm = (struct if_msghdr *)buf; ifm < (struct if_msghdr *)lim;) {
                if (ifm->ifm_msglen == 0) {
-                       log_warn("ifm_msglen is 0 (buf=%p lim=%p ifm=%p)",
+                       log_warnx("ifm_msglen is 0 (buf=%p lim=%p ifm=%p)",
                            buf, lim, ifm);
                        return;
                }
-- 
I'm not entirely sure you are real.