target/user: Only support full command pass-through

After much discussion, give up on only passing a subset of SCSI commands
to userspace and pass them all. Based on what pscsi is doing, make sure
to set SCF_SCSI_DATA_CDB for I/O ops, and define attributes identical to
pscsi.

Make hw_block_size configurable via dev param.

Remove mention of command filtering from tcmu-design.txt.

Signed-off-by: Andy Grover <agrover@redhat.com>
Reviewed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

Documentation/target/tcmu-design.txt

@@ -15,8 +15,7 @@ Contents:
   a) Discovering and configuring TCMU uio devices
   b) Waiting for events on the device(s)
   c) Managing the command ring
-3) Command filtering
-4) A final note
+3) A final note
 
 
 TCM Userspace Design
@@ -364,24 +363,6 @@ int handle_device_events(int fd, void *map)
 }
 
 
-Command filtering
------------------
-
-Initial TCMU support is for a filtered commandset.  Only IO-related
-commands are presented to userspace, and the rest are handled by LIO's
-in-kernel command emulation. The commands presented are all versions
-of:
-
-READ
-WRITE
-WRITE_VERIFY
-XDWRITEREAD
-WRITE_SAME
-COMPARE_AND_WRITE
-SYNCHRONIZE_CACHE
-UNMAP
-
-
 A final note
 ------------