Fix the build with gcc.
Axe ng_fec(4). It has never been a real netgraph(4) module, since
it had no hooks. It has abused ifnet's if_afdata slot and actually
abused every subsystem it touched.

lagg(4) is a proper trunking solution at ifnet(9) layer.

ng_one2many(4) is a proper trunking solution in netgraph(4).
ng_fec(4) removed.
Import the driver for VT-d DMAR hardware, as specified in the revision
1.3 of Intelб╝ Virtualization Technology for Directed I/O Architecture
Specification.  The Extended Context and PASIDs from the rev. 2.2 are
not supported, but I am not aware of any released hardware which
implements them.  Code does not use queued invalidation, see comments
for the reason, and does not provide interrupt remapping services.

Code implements the management of the guest address space per domain
and allows to establish and tear down arbitrary mappings, but not
partial unmapping.  The superpages are created as needed, but not
promoted.  Faults are recorded, fault records could be obtained
programmatically, and printed on the console.

Implement the busdma(9) using DMARs.  This busdma backend avoids
bouncing and provides security against misbehaving hardware and driver
bad programming, preventing leaks and corruption of the memory by wild
DMA accesses.

By default, the implementation is compiled into amd64 GENERIC kernel
but disabled; to enable, set hw.dmar.enable=1 loader tunable.  Code is
written to work on i386, but testing there was low priority, and
driver is not enabled in GENERIC.  Even with the DMAR turned on,
individual devices could be directed to use the bounce busdma with the
hw.busdma.pci<domain>:<bus>:<device>:<function>.bounce=1 tunable.  If
DMARs are capable of the pass-through translations, it is used,
otherwise, an identity-mapping page table is constructed.

The driver was tested on Xeon 5400/5500 chipset legacy machine,
Haswell desktop and E5 SandyBridge dual-socket boxes, with ahci(4),
ata(4), bce(4), ehci(4), mfi(4), uhci(4), xhci(4) devices.  It also
works with em(4) and igb(4), but there some fixes are needed for
drivers, which are not committed yet.  Intel GPUs do not work with
DMAR (yet).

Many thanks to John Baldwin, who explained me the newbus integration;
Peter Holm, who did all testing and helped me to discover and
understand several incredible bugs; and to Jim Harris for the access
to the EDS and BWG and for listening when I have to explain my
findings to somebody.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 month
Remove ng_fec(4).
Remove ng_fec(4).
Fix build. We need to include systm.h before if_var.h.

Pointy hat to:	glebius
Remove ng_fec(4).
Sweep up a bit of arm-land fallout after r257244; include necessary
headers directly that are no longer available via accidental include.
Remove ng_fec.4

Submitted by:	Dmitry Luhtionov <dmitryluhtionov gmail.com>
Remove more remnants of ng_fec(4).

The ng_create_one() and ng_mkpeer() functions in network.subr are
now not used anywhere, but I left them, since they can be useful
in future in netgraph scripting.

Submitted by:	pluknet
repair build for dev/cs.

Reported by: Outback Dingo <outbackdingo@gmail.com>
Quiesce warnings -Wdangling-else

Thanks to jilles for some reviews and tips.
Queisce two category of clang warnings:

1.  missing explicit includes for string.h, stdio.h, etc
2.  missing explicit declaration for some common functions

I have been unable to contact the upstream maintainer for this patch,
http://www.inner.net/opie appears to be the source of truth but it
unreachable
Follow r257244; it's now necessary to include if_var.h.
Remove redundand assignment to error variable and check for its value [1].
Do CTR logging in the case of error as well.

Noted by:	rdivacky [1]
Sponsored by:	The FreeBSD Foundation
MFC after:	1 month
Enable the --sysroot=/foo option in ld by always building with a sysroot
defined. When not building as a cross linker, the sysroot is set to "/".

Exp-run by:	bdrewery (ports/183206)
MFC after:	3 days
Add a couple includes if net/if_var.h that were missed in r257176.
Include <sys/ktr.h>, since we need it if ATH_DEBUG is defined.
Style: s/SYS_EVENTHANDLER_H/_SYS_EVENTHANDLER_H_/g

Submitted by:	bde