MFC r207628,207635:

MFC r207628,207635:
r207628:
  Enable multi-descriptor transmisstion for fragmented mbufs. There
  is no more need to defragment mbufs. After transmitting the
  multi-fragmented frame, the controller updates only the first
  descriptor of multi-descriptor transmission so it's driver's
  responsibility to clear OWN bits of remaining descriptor of
  multi-descriptor transmission. It seems the controller behaves much
  like jme(4) controllers in descriptor handling.

r207635:
  Free entire mbuf chain instead of the first mbuf.

git-svn-id: svn://svn.freebsd.org/base/stable/8@207881 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f