- enable full-duplex mode by default if a device is opened   read-write and it supports full-duplex operation. - update documentation to match this behaviour.
- enable full-duplex mode by default if a device is opened
  read-write and it supports full-duplex operation.
- update documentation to match this behaviour.

see http://marc.info/?l=openbsd-tech&m=118310788926431&w=2 for
more background on this change

"patches look correct to me" marc@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars