use ipv6 global unicast address cc00:101:101::/64 as ipv6 nat address

[everything411]

Currently we use IPV6 unique local address(ULA) fc00:101:101::/64 as out ipv6 NAT address. However, some OSs(i.e. Android) or programs prefer IPV4 address to IPV6 ULA for dual stack domain connection.

The priority for these OSs and programs is IPV6 global unicast address > IPV4 > IPV6 unique local address.

Using an IPV6 unique local address as NAT address can force these OSs to use IPv6 for dual stack domain, which solves the problem.

This PR change fc00:101:101::/64 to cc00:101:101::/64. This address block isn't allocated by IANA so it is safe to use it here.