inet: Add __inet6_scopeid_pton function [BZ #20611]

__inet6_scopeid_pton implements strict validation of numeric scope IDs.
Use it in getaddrinfo and __res_vinit.

inet/net-internal.h

@@ -0,0 +1,30 @@
+/* Network-related functions for internal library use.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _NET_INTERNAL_H
+#define _NET_INTERNAL_H 1
+
+#include <arpa/inet.h>
+#include <stdint.h>
+
+int __inet6_scopeid_pton (const struct in6_addr *address,
+                          const char *scope, uint32_t *result)
+  internal_function attribute_hidden;
+libc_hidden_proto (__inet6_scopeid_pton)
+
+#endif /* _NET_INTERNAL_H */