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

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

Decouple the UUID generator from network interfaces by having MAC
addresses added to the UUID generator using uuid_ether_add(). The
UUID generator keeps an arbitrary number of MAC addresses, under
the assumption that they are rarely removed (= uuid_ether_del()).
This achieves the following:
1. It brings up closer to having the network stack as a loadable
module.
2. It allows the UUID generator to filter MAC addresses for best
results (= highest chance of uniqeness).
3. MAC addresses can come from anywhere, irrespactive of whether
it's used for an interface or not.

A side-effect of the change is that when no MAC addresses have been
added, a random multicast MAC address is created once and re-used if
needed. Previusly, when a random MAC address was needed, it was
created for every call. Thus, a change in behaviour is introduced
for when no MAC addresses exist.

Obtained from: Juniper Networks, Inc.

Add parse_uuid() that creates a binary representation of an UUID from
a string representation.

Move the UUID generator into its own function, called kern_uuidgen(),
so that UUIDs can be generated from within the kernel. The uuidgen(2)
syscall now allocates kernel memory, calls the generator, and does a
copyout() for the whole UUID store. This change is in support of GPT.

/* -> /*- for license, minor formatting changes

Introduce {be,le}_uuid_{enc,dec}() functions for explicitly encoding
and decoding UUID's in big endian and little endian binary format.

Wrap function prototype declarations in __BEGIN_DECLS to do the right thing
with them in non-C cases, outside of the kernel.

Include <sys/cdefs.h> for __BEGIN_DECLS/__END_DECLS as other headers seem
to do in this area.

Requested by: Patrick Hartling <patrick@137.org>

Add uuidgen(2) and uuidgen(1).

The uuidgen command, by means of the uuidgen syscall, generates one
or more Universally Unique Identifiers compatible with OSF/DCE 1.1
version 1 UUIDs.

From the Perforce logs (change 11995):

Round of cleanups:
o Give uuidgen() the correct prototype in syscalls.master
o Define struct uuid according to DCE 1.1 in sys/uuid.h
o Use struct uuid instead of uuid_t. The latter is defined
in sys/uuid.h but should not be used in kernel land.
o Add snprintf_uuid(), printf_uuid() and sbuf_printf_uuid()
to kern_uuid.c for use in the kernel (currently geom_gpt.c).
o Rename the non-standard struct uuid in kern/kern_uuid.c
to struct uuid_private and give it a slightly better definition
for better byte-order handling. See below.
o In sys/gpt.h, fix the broken uuid definitions to match the now
compliant struct uuid definition. See below.
o In usr.bin/uuidgen/uuidgen.c catch up with struct uuid change.

A note about byte-order:
The standard failed to provide a non-conflicting and
unambiguous definition for the binary representation. My initial
implementation always wrote the timestamp as a 64-bit little-endian
(2s-complement) integral. The clock sequence was always written
as a 16-bit big-endian (2s-complement) integral. After a good
nights sleep and couple of Pan Galactic Gargle Blasters (not
necessarily in that order :-) I reread the spec and came to the
conclusion that the time fields are always written in the native
by order, provided the the low, mid and hi chopping still occurs.
The spec mentions that you "might need to swap bytes if you talk
to a machine that has a different byte-order". The clock sequence
is always written in big-endian order (as is the IEEE 802 address)
because its division is resulting in bytes, making the ordering
unambiguous.