Introduce dm_bufio_set_sector_offset() interface to allow setting a
sector offset for a dm-bufio client.  This is a prereq for the DM
integrity target.
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NMilan Broz <gmazyland@gmail.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>