Update CSTP for IPv6 DNS servers

When the Cisco side is configured with IPv4 and IPv6 DNS resolver IPs, it will send option X-CSTP-DNS-IP6 This patch captures the IPv6 addresses provided, and puts them in INTERNAL_IP6_DNS variable for vpnc-scripts (which is already handled there)

Signed-off-by: Colin Petrie colin@spakka.net