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

Make ppp WARNS=5 clean

$Id$ -> $FreeBSD$

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''.

o Fix remaining sizeof problems for 64 bit machines.
o Allow ``set ....'' when we have multiple links but aren't in
multilink mode.
o Do a TLS when we receive a ``Open'' event in ``Closed'' state,
despite the rfc state transition table. This is clearly an
error in the RFC as TLS cannot have yet been called (without
TLF) in the ``Closed'' state.
I've posted a message to comp.protocols.ppp for confirmation.

o De-staticise things that don't need to be static.
o Bring the static ``ttystate'' into struct prompt so that
the tilde context is per prompt and not global.
o Comment the remaining static variables so that it's
clear why they're static.
o Add some XXX comments suggesting that our interface list
and our hostname should be re-generated after a signal
(say SIGUSR1) so that a machine with PCCARDs has a chance.

MFMP: Make ppp multilink capable.
See the file README.changes, and re-read the man page.

Cosmetic (style):
sizeof(var) -> sizeof var
sizeof type -> sizeof(type)

Suggested by: J Wunsch <j@uriah.heep.sax.de>

strncpy(x,y,sizeof(x)) --> strncpy(x,y,sizeof(x)-1)

Suggested by: Philippe Charnier <charnier@lirmm.fr>
Theo de Raadt <deraadt@cvs.openbsd.org>

Add (BSD) copyright headers.

Allow random IP number allocation to peer.
Validate the peers suggested IP by attempting to make a routing table
entry.
Give up IPCP negotiation if the peer NAKs us with an unusable IP.
Always SIOCDIFADDR then SIOCAIFADDR when configuring the tun device.
Using SIOCSIFDSTADDR allows duplicate dst addresses (which we don't
want)!!!
Allow up to 200 interface names (was 50) (now that ppp can play server
properly).
Up the version number (1.5 -> 1.6).

Cosmetic:
Log unexpected CCP packets in the CCP log rather than the ERROR log.
Log unexpected Config Reqs in the appropriate LCP/IPCP/CCP log rather
than the ERROR log.
Log failed route additions and deletions with WARN, not TCPIP.
Log the option id and length for unrecognised IPCP options.
Change some .Sq to .Ar in the man page.