hifn(4) DMA fix for review

[Oleksandr Tymoshenko]

     Proposed patch addresses hifn(4) problems on FreeBSD/mips. Current
implementation keeps some of the state information (indexes in
buffers, etc) in DMA-mapped memory and bus_dma code invalidates them
during sync operations. This fix moves data that doesn't belong to DMA
ring to softc structure.

Patch: http://people.freebsd.org/~gonzo/hifn.diff
Stats for original driver:
     http://people.freebsd.org/~gonzo/hifn.stats.orig.txt
Stats for patched version:
     http://people.freebsd.org/~gonzo/hifn.stats.patched.txt