scsi: target: core: Signal WRITE residuals

According to RFC 7143 11.4.5.2.:

  If SPDTL > EDTL for a task, iSCSI Overflow MUST be signaled in the SCSI
  Response PDU as specified in Section 11.4.5.1.  The Residual Count MUST
  be set to the numerical value of (SPDTL - EDTL).

  If SPDTL < EDTL for a task, iSCSI Underflow MUST be signaled in the SCSI
  Response PDU as specified in Section 11.4.5.1.  The Residual Count MUST
  be set to the numerical value of (EDTL - SPDTL).

libiscsi has residual write tests that check residual kind and residual
amount and all of them (Write10Residuals, Write12Residuals,
Write16Residuals) currently fail.

One of the reasons why they fail is because target completes write commands
with INVALID FIELD IN CDB before setting the Overflow/Underflow bit and
residual amount.

Set the Overflow/Underflow bit and the residual amount before failing a
write to comply with RFC 7143.

Link: https://lore.kernel.org/r/20201203082035.54566-3-a.kovaleva@yadro.com
Signed-off-by: Anastasia Kovaleva <a.kovaleva@yadro.com>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>