MFC r210263,210267,210269-210270:

MFC r210263,210267,210269-210270:
r210263:
  Do not report current link state if interface is not UP.

r210267:
  Add KASSERT to check number of returned DMA segments.

r210269:
  Use bus_get_dma_tag() to get parent tag. Also use
  BUS_SPACE_MAXSIZE_32BIT to specify sum of all segment lengths.
  Previously it used MAXBSIZE which was wrong.

r210270:
  Specify BUS_DMA_ZERO flag to bus_dmamem_alloc(9) and remove bzero()
  calls. Also add BUS_DMA_COHERENT flag to bus_dmamem_alloc(9) to
  take advantage of efficient synchronization for architectures that
  support that feature.

git-svn-id: svn://svn.freebsd.org/base/stable/8@211385 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f