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

Use a cast that doesn't create a compiler warning.

Use __FBSDID() to quiet GCC 3.3 warnings.

Implement the option to disable IPv6 on an sppp interface (counterpart
to the kernel code just committed).

MFC after: 1 month

Clean up half a dozen of header files that are no longer needed now that
we use struct sppp_parms instead of struct sppp for userland programs.

MFC after: 1 month

Userland part of making the LCP restart timer configurable.

Obtained from: i4b (with changes)

Implement knobs to enable/disable VJ header compression.

Submitted by: i4b (modified)
MFC after: 1 month

Include missing header files which define functions for which gcc has
builtins (e.g., exit, strcmp).

$Id$ -> $FreeBSD$

Make buf in authflags a little bigger because 2 strings can be
concatenated and 20 bytes (the old size) is kind of tight.

Make the buf in authflags big enough to hold " norechallenge". I've been
running with this for a few weeks.

Submitted by: someone on the freebsd-isdn maillist

Typo: i. e. -> i.e.
Remove unused #include.

Remove more unused #includes.
Obtained from: Bruce.

Add rcsid. Remove uneeded #include. Use fprintf() in usage() instead of err(3)
to make it print: usage: progname ...

This commit was generated by cvs2svn to compensate for changes in r30302,
which included commits to RCS files with non-trunk default branches.

The spppcontrol(8) utility that is required to set or display things
like PAP and CHAP secrets with sppp(4). This is the first utility
using the new SIOC[SG]IFGENERIC ioctls (and the reason for inventing
them in the first place).