Quieten a toupper() compiler warning.

Gcc complains that an array index is a 'char' when passing a 'char' to
toupper(). Quieten this by coercing to an 'unsigned char'.

Signed-off-by: goldsimon <goldsimon@gmx.de>

src/apps/netbiosns/netbiosns.c

@@ -493,7 +493,7 @@ netbiosns_set_name(const char *hostname)
 
   /* make name into upper case */
   for (i = 0; i < copy_len; i++ ) {
-    netbiosns_local_name[i] = (char)toupper(hostname[i]);
+    netbiosns_local_name[i] = (char)toupper((unsigned char)hostname[i]);
   }
   netbiosns_local_name[copy_len] = '\0';
 }