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

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

Start each of the license/copyright comments with /*-, minor shuffle of lines

$Id$ -> $FreeBSD$

Back out part 1 of the MCFH that changed $Id$ to $FreeBSD$. We are not
ready for it yet.

Make the long-awaited change from $Id$ to $FreeBSD$

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.

Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.

A #define really don't need a ; at the end.

Changes to the Digi/Arnet SYNC driver:

1. Create 2 x 8k transmit buffer blocks in place of the 16k block previously.
With this change the speed as tested with ttcp on a 2Mbit link went up
from 206kbyte/s to 236kbyte/s.
2. Change the rest of the functions to also have the definition of the
return value on a sepperate line.
3. Remove some unused variables.
4. Add code to recover from DMA underruns.
5. Reorder ar_get_packets() to handle errors better.
6. Only allocate a mbuf cluster if the data is more than the mbuf.

(and in a second diff in addition to the above)
7. Stops the occasional DMA underruns that occurred when 2 channels
are running at 2Mbit/s.

Submitted by: John Hay <jhay@mikom.csir.co.za>

This driver supports the Arnet SYNC/570i ISA cards that is based on the
HD64570 chip. Both the 2 and 4 port cards is supported and auto detected.

Line speeds of up to 2Mbps is possible. At this speed about 85% of the
bandwidth is usable with 486DX processors.

The standard FreeBSD sppp code is used for the link level layer. The
default protocol used is PPP. The Cisco HDLC protocol can be used by
adding "link2" to the ifconfig line in /etc/sysconfig or where ever
ifconfig is run.

At the moment only the V.35 and X.21 interfaces is supported. The others
may need tweaks to the clock selection code.

Submitted by: John Hay <jhay@mikom.csir.co.za>