MFC r219701:

MFC r219701:
  Remove too expensive bus_dmamap_sync(9) call in dc_rx_resync().
  With this change, driver may not notice updated descriptor status
  change when bounce buffers are active. However, rxeof() in next run
  will handle the synchronization.

  Change dc_rxeof() a bit to return the number of processed frames in
  RX descriptor ring. Previously it returned the number of frames
  that were successfully passed to upper stack which in turn means it
  ignored frames that were discarded due to errors. The number of
  processed frames in RX descriptor ring is used to detect whether
  driver is out of sync with controller's current descriptor pointer.
  Returning number of processed frames reduces unnecessary (probably
  wrong) re-synchronization.

  Reviewed by:	marius

git-svn-id: svn://svn.freebsd.org/base/stable/8@220083 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f