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

Fix error message.

MFC after: 1 month
Sponsored by: The FreeBSD Foundation

Eliminate unused headers.

Fix handling of queued text and logout requests.

While it may have little sense, text and logout requests can be queued.
If they are, they consume cmdsn, so we should increment our conn_cmdsn.

MFC after: 1 week

Add support for multiple portal groups per target.

This change allows multiple "portal-group" options to be specified per
target. Each of them may include new optional auth-group name parameter
to override per-target auth parameters for specific portal group.

Kernel side support was added earlier at r278161.

MFC after: 2 weeks
Sponsored by: iXsystems, Inc.

Make sequence numbers checks more strict.

While we don't support MCS, hole in received sequence numbers may mean
only PDU loss. While we don't support lost PDU recovery, terminate the
connection to avoid stuck commands.

While there, improve handling of sequence numbers wrap after 2^32 PDUs.

MFC after: 2 weeks

Add discovery-filter. This makes it possible to restrict which targets
are returned during discovery based on initiator portal, name, and CHAP
credentials.

Reviewed by: mav@
MFC after: 1 month
Sponsored by: The FreeBSD Foundation

Clean up (refactor) discovery a little; no functional changes.

MFC after: 1 month
Sponsored by: The FreeBSD Foundation

Make the iSCSI stack use __FBSDID() properly.

MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation

On discovery stage add set of TargetAddress keys to reply, reporting to
the client all the portal groups addresses and ports.

Reviewed by: trasz@
MFC after: 2 weeks
Sponsored by: iXsystems, Inc.

Rename a variable, no functional changes.

Sponsored by: The FreeBSD Foundation

Empty data segment during Login Phase is rather unlikely, but it's
not, by itself, a protocol error. This fixes interoperability with
OpenBSD initiator.

Sponsored by: The FreeBSD Foundation

Bring in the new iSCSI target and initiator.

Reviewed by: ken (parts)
Approved by: re (delphij)
Sponsored by: FreeBSD Foundation