MFC: r239089

MFC: r239089

- Merge from NetBSD:
  When issuing a non-DMA command, make sure to set the "remaining length of
  command to be transferred via DMA" (sc_cmdlen) to zero up-front, otherwise
  we might get confused on command competition interrupt (no DMA active but
  still data left to transfer).
- Implement handling of MSG_IGN_WIDE_RESIDUE which some targets produce, as
  just rejecting these leads to a resend and disconnect loop.
  Reported and tested by: mjacob

git-svn-id: svn://svn.freebsd.org/base/stable/8@239490 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f