Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

libkvm code janitoring

- make WARNS=6 clean for archs w/o strict alignment requirments
- add const, ANSIfy, remove unused vars, cast types for comparison
- thanks to differing definitions of VM_MIN_ADDRESS across our archs, we
need to trick the compiler to not complain about signedness. We could
either fix VM_MIN_ADDRESS to always be a simple integer or make the
check conditional on $ARCH.

Closes PRs: kern/42386, kern/83364
Reviewed by: bde

Fix typo in comment.

MFC after: 3 days

Rather than replicating the maths from the kernel, use the
value the kernel calculated directly as we already read it
with struct vnet. This will make kvm_vnet.c more resilent
in case of possible kernel changes.

Reviewed by: rwatson
Approved by: re (kib)

Merge the remainder of kern_vimage.c and vimage.h into vnet.c and
vnet.h, we now use jails (rather than vimages) as the abstraction
for virtualization management, and what remained was specific to
virtual network stacks. Minor cleanups are done in the process,
and comments updated to reflect these changes.

Reviewed by: bz
Approved by: re (vimage blanket)

Make libkvm work on live systems and crashdumps with and
without VIMAGE virtualization in the kernel.

If we cannot resolve a symbol try to see if we can find it with
prefix of the virtualized subsystem, currently only "vnet_entry"
by identifying either the vnet of the current process for a
live system or the vnet of proc0 (or of dumptid if compiled
in a non-default way).

The way this is done currently allows us to only touch libkvm
but no single application. Once we are going to virtualize more
subsystems we will have to review this decision for better scaling.

Submitted by: rwatson (initial version of kvm_vnet.c, lots of ideas)
Reviewed by: rwatson
Approved by: re (kib)