rpl-border-router: fix GCC 8 warnings

GCC 8 added the -Wstringop-truncation warning
which makes the regression tests fail on recent
versions of Ubuntu. Silence the compiler by
copying one character less, and add an explicit
null termination afterwards when required.

examples/rpl-border-router/webserver/httpd-simple.c

@@ -175,7 +175,8 @@ PT_THREAD(handle_input(struct httpd_state *s))
     s->filename[sizeof(s->filename) - 1] = '\0';
   } else {
     s->inputbuf[PSOCK_DATALEN(&s->sin) - 1] = 0;
-    strncpy(s->filename, s->inputbuf, sizeof(s->filename));
+    strncpy(s->filename, s->inputbuf, sizeof(s->filename) - 1);
+    s->filename[sizeof(s->filename) - 1] = '\0';
   }
 #endif /* URLCONV */
 

os/services/rpl-border-router/native/slip-config.c

@@ -97,10 +97,11 @@ slip_config_handle_arguments(int argc, char **argv)
 
     case 't':
       if(strncmp("/dev/", optarg, 5) == 0) {
-        strncpy(slip_config_tundev, optarg + 5, sizeof(slip_config_tundev));
+        strncpy(slip_config_tundev, optarg + 5, sizeof(slip_config_tundev) - 1);
       } else {
-        strncpy(slip_config_tundev, optarg, sizeof(slip_config_tundev));
+        strncpy(slip_config_tundev, optarg, sizeof(slip_config_tundev) - 1);
       }
+      slip_config_tundev[sizeof(slip_config_tundev) - 1] = '\0';
       break;
 
     case 'a':

os/services/rpl-border-router/native/tun-bridge.c

@@ -165,7 +165,7 @@ tun_alloc(char *dev)
    */
   ifr.ifr_flags = IFF_TUN | IFF_NO_PI;
   if(*dev != 0) {
-    strncpy(ifr.ifr_name, dev, IFNAMSIZ);
+    strncpy(ifr.ifr_name, dev, IFNAMSIZ - 1);
   }
 
   if((err = ioctl(fd, TUNSETIFF, (void *)&ifr)) < 0) {