MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Consider PROTO_IPV6 as compressible by CCP.

Spotted by: Nick Sayer <nsayer@quack.kfu.com>

o Add ipv6 support, abstracting most NCP addresses into opaque
structures (well, they're treated as opaque).

It's now possible to manage IPv6 interface addresses and routing
table entries and to filter IPV6 traffic whether encapsulated or
not.

IPV6CP support is crude for now, and hasn't been tested against
any other implementations.

RADIUS and IPv6 are independent of eachother for now.

ppp.linkup/ppp.linkdown aren't currently used by IPV6CP

o Understand all protocols(5) in filter rules rather than only a select
few.

o Allow a mask specification for the ``delete'' command. It's now
possible to specifically delete one of two conflicting routes.

o When creating and deleting proxy arp entries, do it for all IPv4
interface addresses rather than doing it just for the ``current''
peer address.

o When iface-alias isn't in effect, don't blow away manually (via ``iface
add'') added interface addresses.

o When listening on a tcp server (diagnostic) socket, bind so that a
tcp46 socket is created -- allowing both IPv4 and IPv6 connections.

o When displaying ICMP traffic, don't display the icmp type twice.
When display traffic, display at least some information about unrecognised
traffic.

o Bump version

Inspired after filtering work by: Makoto MATSUSHITA <matusita@jp.FreeBSD.org>

Convert IIJ copyrights to BSD copyrights.

Approved by: Toshiharu OHNO <tohno@sirius.ocn.ne.jp>

$Id$ -> $FreeBSD$

o Redesign the layering mechanism and make the aliasing code part of
the layering.

We now ``stack'' layers as soon as we open the device (when we figure
out what we're dealing with). A static set of `dispatch' routines are
also declared for dealing with incoming packets after they've been
`pulled' up through the stacked layers.

Physical devices are now assigned handlers based on the device type
when they're opened. For the moment there are three device types;
ttys, execs and tcps.

o Increment version number to 2.2
o Make an entry in [uw]tmp for non-tty -direct invocations (after
pap/chap authentication).
o Make throughput counters quad_t's
o Account for the absolute number of mbuf malloc()s and free()s in
``show mem''.
o ``show modem'' becomes ``show physical''.