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

Drop group privileges after opening the kvm descriptor, otherwise, the code
would not drop privileges as expected.

While there also add checks for the drop and bail out immediately if we
failed.

MFC after: 3 days

Check l2cap socket initialisation and define L2CAP_SOCKET_CHECKED
This will fix build.

Stop including if_var.h from userland.

Sponsored by: Nginx, Inc.

Merge from projects/sendfile:

o Introduce a notion of "not ready" mbufs in socket buffers. These
mbufs are now being populated by some I/O in background and are
referenced outside. This forces following implications:
- An mbuf which is "not ready" can't be taken out of the buffer.
- An mbuf that is behind a "not ready" in the queue neither.
- If sockbet buffer is flushed, then "not ready" mbufs shouln't be
freed.

o In struct sockbuf the sb_cc field is split into sb_ccc and sb_acc.
The sb_ccc stands for ""claimed character count", or "committed
character count". And the sb_acc is "available character count".
Consumers of socket buffer API shouldn't already access them directly,
but use sbused() and sbavail() respectively.
o Not ready mbufs are marked with M_NOTREADY, and ready but blocked ones
with M_BLOCKED.
o New field sb_fnrdy points to the first not ready mbuf, to avoid linear
search.
o New function sbready() is provided to activate certain amount of mbufs
in a socket buffer.

A special note on SCTP:
SCTP has its own sockbufs. Unfortunately, FreeBSD stack doesn't yet
allow protocol specific sockbufs. Thus, SCTP does some hacks to make
itself compatible with FreeBSD: it manages sockbufs on its own, but keeps
sb_cc updated to inform the stack of amount of data in them. The new
notion of "not ready" data isn't supported by SCTP. Instead, only a
mechanical substitute is done: s/sb_cc/sb_ccc/.
A proper solution would be to take away struct sockbuf from struct
socket and allow protocols to implement their own socket buffers, like
SCTP already does. This was discussed with rrs@.

Sponsored by: Netflix
Sponsored by: Nginx, Inc.

Fix build

Make sure Bluetooth stuff can be compiled on amd64

Submitted by: ps

Include <nlist.h> for nlist-related declarations instead of depending on
namespace pollution in <kvm.h>.

Update Bluetooth code.

Reviewed by: M. Warner Losh <imp@bsdimp.com>; John Hay <jhay@freebsd.org>
Approved by: M. Warner Losh <imp@bsdimp.com> (mentor)

Part one of undating the bluetooth code to the newest version

Submitted by: Maksim Yevmenkin <m_evmenkin@yahoo.com>
Approved by: re@

The second try a committing the bluetooth code
Has been seen to work on several cards and communicating with
several mobile phones to use them as modems etc.

We are still talking with 3com to try get them to allow us to include
the firmware for their pccard in the driver but the driver is here..
In the mean time
it can be downloaded from the 3com website and loaded using the utility
bt3cfw(8) (supplied) (instructions in the man page)

Not yet linked to the build

Submitted by: Maksim Yevmenkin <myevmenk@exodus.net>
Approved by: re