Introduce lwip_toupper and use it in netbiosns.c

This fixes build error when LWIP_NO_CTYPE_H=1.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Simon Goldschmidt <goldsimon@gmx.de>

src/apps/netbiosns/netbiosns.c

@@ -499,7 +499,7 @@ netbiosns_set_name(const char *hostname)
 
   /* make name into upper case */
   for (i = 0; i < copy_len; i++ ) {
-    netbiosns_local_name[i] = (char)toupper((unsigned char)hostname[i]);
+    netbiosns_local_name[i] = (char)lwip_toupper(hostname[i]);
   }
   netbiosns_local_name[copy_len] = '\0';
 }