CFT: msk(4) 64bit DMA support

Hi,

Here is a patch that implements 64bit DMA on msk(4). If you use
msk(4) on a system that has more than 4GB memory, please try the
patch at the following URL and let me know whether it works or not.
You need latest msk(4) in HEAD to apply the patch.
http://people.freebsd.org/~yongari/msk/msk.64bit.dma.diff

Previously msk(4) may have used bounce buffers on systems that have
more than 4GB memory. You can verify whether msk(4) is using bounce
buffers by checking the output of "sysctl hw.busdma". For instance,
hw.busdma.zone0.total_bounced counter would increase while network
operation is in progress.  If patch above works you wouldn't see
the counter change anymore and it would also enhance network
performance since it wouldn't have to copy from or to bounce
buffers.

Thanks.