libnetwork: Replace some basic inet_* functions with the musl versions.

This beings the replacement of the libbind/netresolv-based implementation
with musl's equivalent. The code is less well commented in some places,
but it is well-designed and well-maintained, and the licensing situation
is much cleaner than the multi-BSD-licensed libbind-derivative code,
as well as being actively maintained (supposedly NetBSD has taken over
libbind/netresolv, but have not posted any portable code since 2013.)

The eventual goal is to replace the entirety of NetResolv with code
from musl, which will be an involved process as ABI compatibility
will be a problem. These functions at least are extremely
straightforward to replace.

Change-Id: Icfefaa90cbf56b012e4e42360be5b0f0c16d73bf
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2943
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
Reviewed-by: Axel Dörfler <axeld@pinc-software.de>