fix proplib deprecation

Cosmetic: s/xenv/oenv/

Only describe flags -L and -m in the usage if they are available.
That helps me get rid of some conditional compilation (INET6) in
ifconfig.

Let each protocol/feature-module print its own usage, so that the
ifconfig usage reflects the modules that are actually compiled-in.

Write usage information for carp(4) options.

Let us add/remove features from ifconfig, such as support for
various address families (inet, inet6, iso, atalk) and protocols
(802.11, 802.3ad, CARP), simply by trimming the list of sources in
the Makefile. This helps one customize ifconfig for an embedded
device or for install media, and it eliminates a lot of grotty
#ifdef'age. Now, the ifconfig syntax and semantics are finalized
at run-time using the constructor routines in each address-family/protocol
module.

(In principle, ifconfig could load virtually all of its syntax from
shared objects.)

Extract a lot of common code into subroutines, in order to shrink
the ifconfig binary a bit. Make all of the address families share
code for address addition/replacement/removal, and delete "legacy"
code for manipulating addresses. That may have broken atalk and
iso, despite my best efforts.

Extract an include file, Makefile.inc, containing the make-fu that
both ifconfig and x_ifconfig share.

Sprinkle static. Change some int's to bool's. Constify.

Add RCS Ids to carp.c and env.c. Move media code to a new file,
media.c. Delete several unneeded header files.

Set, reset, and display the IEEE 802.11 attribute, 'dot11RTSThreshold'.

Bug fix: do not require both a interface address and a destination
address for point-to-point interfaces, but accept a interface
address by itself.

Fix two bugs:

1 Let us associate a keyword with either a signed or an unsigned
number. Associate the '-chan' keyword with an unsigned number.
This fixes the defect that crashed 'ifconfig wi0 -chan', reported
by Michael van Elst.

2 Do not try to interpret names as ISO addresses unless the ISO
address family was specified. iso_addr(3) does not report errors,
so it appears to interpret *everything* as an ISO address. This
is a stopgap fix for the defect in 'ifconfig lo0 inet6' on a
!INET6 kernel that deletes the first IPv4 address on lo0.
(Reported by Scott Ellis.)

Repair agr(4) syntax. Should fix PR bin/38600.

Factor out common code, creating direct_ioctl() and indirect_ioctl()
for the two most prevalent styles of ioctl(2) calls in ifconfig(8).

Move net80211 and agr(4) syntax out of ifconfig.c and into ieee80211.c
and agr.c, respectively.

branches: 1.8.2;
agrsetport: fix a use of uninitialized variable.

Use prop_dictionary_util(3).

Use prop_dictionary_util(3) some more.

When we read interface flags and capabilities from the kernel, take
care not to record them in our current environment (env), but record
them in the output environment (oenv), instead. This helps us get
interface capabilities and flags right.

Overhaul ifconfig. Use fewer global variables. Take a leap toward
improved modularity and extensibility.

In the new architecture, a directed graph of argument-matching
objects (match objects) expresses the set of feasible ifconfig
statements. Match objects are labelled by subroutines that provide
the statement semantics.

Many IPv4, IPv6, 802.11, tunnel, and media configurations have been
tested.

AppleTalk, ISO, carp(4), agr(4), and vlan(4) configuration need
testing.

Copy a const string to a temporary buffer instead of using __UNCONST().

Cosmetic: get rid of superflous curly braces and cast to (void *).

branches: 1.3.20; 1.3.22;
name -> ifname (avoid shadow decl with global name[]).

Move extern decls to extern.h

add agr(4), a pseudo network device driver for link aggregation.