Update mud

src/main.c

@@ -437,12 +437,14 @@ int main (int argc, char **argv)
                     unsigned char *data = &buf[ic.hdr_size];
                     if (data[0]==3) {
                         int new_mtu = (data[6]<<8)|data[7];
+                        if (new_mtu) {
                             gt_log("received MTU from ICMP: %i\n", new_mtu);
                             mud_set_mtu(mud, new_mtu-50);
                         }
                     }
                 }
             }
+        }
 
         if (mud_is_up(mud)) {
             if (!started) {