When client address is received, IPv6 address could be specified without
square brackets and without port, as well as both with the brackets and
port.  The change allows IPv6 in square brackets and no port, which was
previously considered an error.  This format conforms to RFC 3986.

The change also affects proxy_bind and friends.

When re-creating a non-reusable zone, make the pointer to the old zone
available during the new zone initialization.

Previously chain links could sometimes be dropped instead of being reused,
which could result in increased memory consumption during long requests.

A similar chain link issue in ngx_http_gzip_filter_module was fixed in
da46bfc484ef (1.11.10).

Based on a patch by Sangmin Lee.