libnetwork: Synchronize netresolv with NetBSD 9.3.

Some of the Haiku-specific modifications that were previously unmarked
are now clearly marked with #ifdef __HAIKU__.

BIND9-specific files containing private APIs never exposed in public
headers have been removed.

Tested with wget, curl, pkgman (Network Kit), WebPositive (WebKit/curl),
and Falkon (QtWebEngine/Chromium). All DNS-related operations seem
to still work just fine.

(One patch also imported from NetBSD trunk for GCC 12+ compatibility.)

Change-Id: I4a349577b24b4df008fd9cba5d3a322cd24397f1
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6879
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

arpa/nameser.h: Cleanup.

* Remove functions not even FreeBSD defines.
* Remove dependency on unnecessary headers.
* Update copyright headers to match FreeBSD's; includes
removal of the advertising clause.
* Move some private structs to netresolv port_before.

Unfortunately, it seems musl implements very little of this file,
so we may wind up sticking with netresolv for its implementation.

netresolv: enable weak symbols

It's simpler to have these around, they allow autotools to find the
functions the regular way (using AC_SEARCH_LIBS) as the autotools don't
use the include file and can't see the #define we are putting there to
redirect to the __ prefixed version of the methods.

Change-Id: I6a9743e88503fbdcba98e276375bc11f73a64411
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1889
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

libnetwork: Move from src/kits to src/system.

Properly speaking, this is part of POSIX and not of the Be-style
"kits", and so it should live in system/ alongside libroot.
No functional change intended.

Change-Id: I0fcf78a09c76e220ad4f1719d147978ef4a3bc52
Reviewed-on: https://review.haiku-os.org/726
Reviewed-by: Axel Dörfler <axeld@pinc-software.de>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>