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

Get closer to a VIMAGE network stack teardown from top to bottom rather
than removing the network interfaces first. This change is rather larger
and convoluted as the ordering requirements cannot be separated.

Move the pfil(9) framework to SI_SUB_PROTO_PFIL, move Firewalls and
related modules to their own SI_SUB_PROTO_FIREWALL.
Move initialization of "physical" interfaces to SI_SUB_DRIVERS,
move virtual (cloned) interfaces to SI_SUB_PSEUDO.
Move Multicast to SI_SUB_PROTO_MC.

Re-work parts of multicast initialisation and teardown, not taking the
huge amount of memory into account if used as a module yet.

For interface teardown we try to do as many of them as we can on
SI_SUB_INIT_IF, but for some this makes no sense, e.g., when tunnelling
over a higher layer protocol such as IP. In that case the interface
has to go along (or before) the higher layer protocol is shutdown.

Kernel hhooks need to go last on teardown as they may be used at various
higher layers and we cannot remove them before we cleaned up the higher
layers.

For interface teardown there are multiple paths:
(a) a cloned interface is destroyed (inside a VIMAGE or in the base system),
(b) any interface is moved from a virtual network stack to a different
network stack ("vmove"), or (c) a virtual network stack is being shut down.
All code paths go through if_detach_internal() where we, depending on the
vmove flag or the vnet state, make a decision on how much to shut down;
in case we are destroying a VNET the individual protocol layers will
cleanup their own parts thus we cannot do so again for each interface as
we end up with, e.g., double-frees, destroying locks twice or acquiring
already destroyed locks.
When calling into protocol cleanups we equally have to tell them
whether they need to detach upper layer protocols ("ulp") or not
(e.g., in6_ifdetach()).

Provide or enahnce helper functions to do proper cleanup at a protocol
rather than at an interface level.

Approved by: re (hrs)
Obtained from: projects/vnet
Reviewed by: gnn, jhb
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D6747

Check that hhk_helper pointer isn't NULL before access.

It isn't forbidden to use NULL pointer for hook_helper in hookinfo
structure when hhook_add_hook() adds new helper hook.

Move hhook's per-vnet initialisation to an earlier SYSINIT SI_SUB stage to
ensure all per-vnet related hhook initialisation is completed prior to any
virtualised hhook points attempting registration.

vnet_register_sysinit() requires that a stage later than SI_SUB_VNET be chosen.
There are no per-vnet initialisors in the source tree at this time which run
earlier than SI_SUB_INIT_IF. A quick audit of non-virtualised SYSINITs indicates
there are no subsystems pre SI_SUB_MBUF that would likely be interested in
registering a virtualised hhook point.

Settle on SI_SUB_MBUF as hhook's per-vnet initialisation stage as it's the first
overtly network-related initilisation stage to run after SI_SUB_VNET. If a
subsystem that initialises earlier than SI_SUB_MBUF ends up wanting to register
virtualised hhook points in future, hhook's use of SI_SUB_MBUF will need to be
revisited and would probably warrant creating a dedicated SI_SUB_HHOOK which
runs immediately after SI_SUB_VNET.

MFC after: 1 week

Add a private KPI between hhook and khelp that allows khelp modules to insert
hook functions into hhook points which register after the modules were loaded -
potentially useful during boot or if hhook points are dynamically registered.

MFC after: 1 week

Internalise handling of virtualised hook points inside
hhook_{add|remove}_hook_lookup() so that khelp (and other potential API
consumers) do not have to care when they attempt to (un)hook a particular hook
point identified by id and type.

Reviewed by: scottl
MFC after: 1 week

Fix a major oversight in r251732 which causes non-VIMAGE kernels to trigger a
KASSERT during TCP hhook registration at boot. Virtualised hook points only
require extra housekeeping and sanity checking when "options VIMAGE" is present.

Reported by: bdrewery,jh,dhw
Tested by: dhw
MFC after: 1 week
X-MFC with: 251732

Add support for non-virtualised hhook points, which are uniquely identified by
type and id, as compared to virtualised hook points which are now uniquely
identified by type, id and a vid (which for vimage is the pointer to the vnet
that the hhook resides in).

All hhook_head structs for both virtualised and non-virtualised hook points
coexist in hhook_head_list, and a separate list is maintained for hhook points
within each vnet to simplify some vimage-related housekeeping.

Reviewed by: scottl
MFC after: 1 week

Fix a potential NULL-pointer dereference that would trigger if the hhook
registration site did not provide storage for a copy of the hhook_head struct.

MFC after: 3 days

Staticize malloc types.

Approved by: lstewart
MFC after: 1 week

Use the full and proper company name for Swinburne University of Technology
throughout the source tree.

Requested by: Grenville Armitage, Director of CAIA at Swinburne University of
Technology
MFC after: 3 days

Fix hhook_head_is_virtualised() so that "ret" can't be used uninitialised.

Sponsored by: FreeBSD Foundation
Submitted by: pjd
MFC after: 9 weeks
X-MFC with: r216615

Fix some minor style/readability nits in hhook.

Sponsored by: FreeBSD Foundation
Submitted by: pjd
MFC after: 9 weeks
X-MFC with: r216615

- Introduce the Hhook (Helper Hook) KPI. The KPI is closely modelled on pfil(9),
and in many respects can be thought of as a more generic superset of pfil.
Hhook provides a way for kernel subsystems to export hook points that Khelp
modules can hook to provide enhanced or new functionality to the kernel. The
KPI has been designed to ensure hook points pose no noticeable overhead when
no hook functions are registered.

- Introduce the Khelp (Kernel Helpers) KPI. Khelp provides a framework for
managing Khelp modules, which indirectly use the Hhook KPI to register their
hook functions with hook points of interest within the kernel. Khelp modules
aim to provide a structured way to dynamically extend the kernel at runtime in
an ABI preserving manner. Depending on the subsystem providing hook points, a
Khelp module may be able to associate per-object data for maintaining relevant
state between hook calls.

- pjd's Object Specific Data (OSD) KPI is used to manage the per-object data
allocated to Khelp modules. Create a new "OSD_KHELP" OSD type for use by the
Khelp framework.

- Bump __FreeBSD_version to 900028 to mark the introduction of the new KPIs.

In collaboration with: David Hayes <dahayes at swin edu au> and
Grenville Armitage <garmitage at swin edu au>
Sponsored by: FreeBSD Foundation
Reviewed by: bz, others along the way
MFC after: 3 months