This patch is preparation for fixing alloc_len overrun in SENSE 6/10 and
READCAP 6/10. To simplify code forbid usage of iov outside of
scsi/task.c.
This also drop SPDK_SCSI_TASK_ALLOC_BUFFER flag that obfuscate code. As
a replacement assume that if field alloc_len is non zero it mean that
iov.buffer is internally allocated. Functions
spdk_scsi_task_free_data(), spdk_scsi_task_set_data() and
spdk_scsi_task_alloc_data() manage this field.
Change-Id: Ife357a5bc36121f93a4c5d259b9a5a01559e7708
Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>