Update changelog

Update changelog

This also addresses the closely-related issue described in
https://gitlab.com/openconnect/openconnect/-/merge_requests/500, where
OpenConnect would prefer a GP server's IPv6 magic ping adress over its
Legacy IP magic ping address, even if `--disable-ipv6` is specified:
> Previous logic always preferred the ipv6 gateway address and magic for ESP
> even if ipv6 was explicitly disabled.  A VPN I use currently will only
> negotiate an ESP connection over ipv4 despite advertising a v6 gateway.

This similarly results in non-functional ESP:

> The result was that with ipv6 enabled, ESP pings were sent but would not
> renegotiate, with it disabled openconnect would erroneously report that
> the response did not contain a matching gateway and keys.

Signed-off-by: Daniel Lenski <dlenski@gmail.com>