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

Add __unused. Ansi prototypes.

Silence GCC4 signed/unsigned pointer mismatch warning.

Style: space after "return".

Unnest includes before forthcoming editing.

Get rid of all (but one in write.c) static size buffers.

Get rid of the old constants which did not include the trailing NUL
and use the new constants which do.

When the 'msg' command is used from the command line, check for a
synchronous reply, and display it (if any) before exiting.

Requested by: phk

Remove erroneous built-in help information for the 'msg' command.

Add two new generic control messages, NGM_ASCII2BINARY and
NGM_BINARY2ASCII, which convert control messages to ASCII and back.
This allows control messages to be sent and received in ASCII form
using ngctl(8), which makes ngctl a lot more useful.

This also allows all the type-specific debugging code in libnetgraph
to go away -- instead, we just ask the node itself to do the ASCII
translation for us.

Currently, all generic control messages are supported, as well as
messages associated with the following node types: async, cisco,
ksocket, and ppp.

See /usr/share/examples/netgraph/ngctl for an example of using this.

Also give ngctl(8) the ability to print out incoming data and
control messages at any time. Eventually nghook(8) may be subsumed.

Several other misc. bug fixes.

Reviewed by: julian