Reviewed-by: NRichard Levitte <levitte@openssl.org>

Reviewed-by: NRichard Levitte <levitte@openssl.org>

Adds a new function BIO_ADDR_clear to reset a BIO_ADDR back to an
unitialised state, and to set the family to AF_UNSPEC.
Reviewed-by: NViktor Dukhovni <viktor@openssl.org>

Because different platforms have different levels of support for IPv6,
different kinds of sockaddr variants, and some have getaddrinfo et al
while others don't, we could end up with a mess if ifdefs, duplicate
code and other maintainance nightmares.

Instead, we're introducing wrappers around the common form for socket
communication:
BIO_ADDR, closely related to struct sockaddr and some of its variants.
BIO_ADDRINFO, closely related to struct addrinfo.

With that comes support routines, both convenient creators and
accessors, plus a few utility functions:

BIO_parse_hostserv, takes a string of the form host:service and
splits it into host and service.  It checks for * in both parts, and
converts any [ipv6-address] syntax to ust the IPv6 address.

BIO_lookup, looks up information on a host.

All routines handle IPv4 (AF_INET) and IPv6 (AF_INET6) addresses, and
there is support for local sockets (AF_UNIX) as well.
Reviewed-by: NKurt Roeckx <kurt@openssl.org>