Add missing test for interface being up.

Thanks to Dave Taht.

message.c

@@ -1172,6 +1172,9 @@ really_send_update(struct interface *ifp, const unsigned char *id,
                    unsigned short seqno, unsigned short metric,
                    unsigned char *channels, int channels_len)
 {
+    if(!if_up(ifp))
+        return;
+
     if((ifp->flags & IF_UNICAST) != 0) {
         struct neighbour *neigh;
         FOR_ALL_NEIGHBOURS(neigh) {