Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Merge r227738, r228574:
Fill in sin_family in ioctl() arguments.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

If compiling RESCUE always ignore feature_present(3) calls so that
a /rescue/ifconfig more modern than the kernel could still configure
IPv4 or IPv6 addresses.

Reported by: Andrzej Tobola (ato iem.pw.edu.pl)
Reported by: gcooper
MFC after: 1 day
X-MFC: will not MFC any time soon, just reminder for r222527

Conditionally compile in the af_inet and af_inet6, af_nd6 modules.
If compiled in for dual-stack use, test with feature_present(3)
to see if we should register the IPv4/IPv6 address family related
options.

In case there is no "inet" support we would love to go with the
usage() and make the address family mandatory (as it is for anything
but inet in theory). Unfortunately people are used to
ifconfig IF up/down
etc. as well, so use a fallback of "link". Adjust the man page
to reflect these minor details.

Improve error handling printing a warning in addition to the usage
telling that we do not know the given address family in two places.

Reviewed by: hrs, rwatson
Sponsored by: The FreeBSD Foundation
Sponsored by: iXsystems
MFC after: 2 weeks

Reject invalid CIDR widths rather than silently stopping at the first
non-digit character.

Due to an issue with rc(8) in a test configuration, ifconfig was being
invoked with the address used again as the width - for example,

ifconfig vlan0 10.0.0.1/10.0.0.1

Prior to this change, that address/width would be interpreted as
10.0.0.1/10.

- Use size_t instead of int when appropriate;
- Use C99 sparse initialization.

With these changes ifconfig(8) is WARNS=2 clean.

The structs ifaliasreq and in_aliasreq have exactly the same layout and
member names, but we really do mean to use in_aliasreq here.

MFC after: 1 week

use getifaddrs from libc instead of private code

Reviewed by: bms
MFC after: 1 month

only show a tunnel information of an adequate address family.

Approved by: re (dwhite)

Overhaul to cleanup some of the tangled logic that's grown over the years.

o break per-address family support out into separate files
o modularize per-address family and functional operations using
a registration mechanism; this permits configuration according
to which files you include (but beware that order of the files
is important to insure backwards compatibility)
o many cleanups to eliminate incestuous behaviour, global variables,
and poor coding practices (still much more to fix)

The original motivation of this work was to support dynamic addition
of functionality based on the interface so we can eliminate the various
little control programs and so that vendors can distribute ifconfig
plugins that support their in-kernel code. That work is still to be
completed.

o Update 802.11 support for all the new net80211 functionality; some
of these operations (e.g. list *) may be better suited in a different
program