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.

Previously, it could result when left-shifting signed integer due to implicit
integer promotion, such that the most significant bit appeared on the sign bit.

In practice, though, this results in the same left value as with an explicit
cast, at least on known compilers, such as GCC and Clang.  The reason is that
in_addr_t, which is equivalent to uint32_t and same as "unsigned int" in ILP32
and LP64 data type models, has the same type width as the intermediate after
integer promotion, so there's no side effects such as sign-extension.  This
explains why adding an explicit cast does not change object files in practice.

Found with UndefinedBehaviorSanitizer (shift).

Based on a patch by Piotr Sikora.