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

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

Assume the link to be dead if bit error rate (BER) parameter is set to 1.
When a transition from link alive to link dead configuration or vice
versa occurs, notify any upstream and / or downstream peers using
NGM_FLOW messagges.

Link state notification using NGM_FLOW messages is modelled around
around already existing code in ng_ether.c.

MFC after: 3 days

Node constructor methods are supposed to be called in syscall
context always. Convert nodes to consistently use M_WAITOK flag
for memory allocation.

Reviewed by: julian

Simplify ng_pipe locking model by relying on the netgraph framework
to provide serialization of calls into the node, which is accomplished
by markng the node as single-threaded (NGF_FORCE_WRITER).

The price we pay is that each ng_pipe instance now has its own callout
handler which polls for queued frames on each clock tick, as long as
the pipe has any frames in its internal queues. OTOH, we got rid of
the global ng_pipe mutex, so from now on multiple ng_pipe instances
can operate in parallel. This change also fixes counting of forwarded
frames when an ng_pipe node is not enforcing any packet impairments.

While here, attempt to improve adherance to style(9) throughout
otherwise mostly unreadable code.

MFC after: 3 days

Fix a double-free bug which can occur if both bit error rate and packet
duplication probability are configured on a ng_pipe node.

Submitted by: Jeffrey Ahrenholtz
MFC after: 3 days

Avoid undefined behaviour.

Reviewed by: zec@

Start copyright notice with /*-

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)

Retire the MALLOC and FREE macros. They are an abomination unto style(9).

MFC after: 3 months

Add Marko's pipe node.
This allows one to do flow modulation similar to dummynet
between arbitrary nodes.