MFC revision 199069:

MFC revision 199069:

Initialize the whole message unit's DMA buffer to zero, this fixes a panic
during boot when ARC1200 is being used with certain motherboard models.

This commit brings the driver to the same state of vendor's 1.20.00.16
release.  Many thanks to Areca for their continued support to FreeBSD.

This instant MFC was requested by re@ (kensmith) in preparation for
8.0-RC3.

Reported by:	Jirka Mikulas <jiri mikulas com>
Submitted by:	Erich Chen (Areca)

git-svn-id: svn://svn.freebsd.org/base/stable/8@199120 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f