If the client sends "X-CSTP-Full-IPv6-Capability: true", then we
use the headers:
X-CSTP-Address-IP6: 2001:db8:1000:1000::1/64
X-CSTP-Split-Include-IP6: 2001:db8:1000:1001::/64
X-CSTP-Split-Include-IP6: 2001:db8:1000:1002::/64
(see corresponding openconnect change)
This patch also combines ipv4-dns and ipv6-dns options
that are now handled as aliases to dns.
A side-effect of this patch is that the local keyword is no
longer supported.