- MFC r196370.

- MFC r196370.
  Do not try to reevaluate current RX production index on each
  loop iteration as it can be updated by the card while we
  process the RX ring forcing us to process RX descriptors
  for which DMA synchronisation operation has not been
  performed.  This fixes the bug when bge(4) drops packets
  under high load.

Discussed with:	yongari, marius
Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/8@196371 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f