scsi: zfcp: fix queuecommand for scsi_eh commands when DIX enabled

Since commit db007fc5 ("[SCSI] Command protection operation"),
scsi_eh_prep_cmnd() saves scmd->prot_op and temporarily resets it to
SCSI_PROT_NORMAL.
Other FCP LLDDs such as qla2xxx and lpfc shield their queuecommand()
to only access any of scsi_prot_sg...() if
(scsi_get_prot_op(cmd) != SCSI_PROT_NORMAL).

Do the same thing for zfcp, which introduced DIX support with
commit ef3eb71d ("[SCSI] zfcp: Introduce experimental support for
DIF/DIX").

Otherwise, TUR SCSI commands as part of scsi_eh likely fail in zfcp,
because the regular SCSI command with DIX protection data, that scsi_eh
re-uses in scsi_send_eh_cmnd(), of course still has
(scsi_prot_sg_count() != 0) and so zfcp sends down bogus requests to the
FCP channel hardware.

This causes scsi_eh_test_devices() to have (finish_cmds == 0)
[not SCSI device is online or not scsi_eh_tur() failed]
so regular SCSI commands, that caused / were affected by scsi_eh,
are moved to work_q and scsi_eh_test_devices() itself returns false.
In turn, it unnecessarily escalates in our case in scsi_eh_ready_devs()
beyond host reset to finally scsi_eh_offline_sdevs()
which sets affected SCSI devices offline with the following kernel message:

"kernel: sd H:0:T:L: Device offlined - not ready after error recovery"
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Fixes: ef3eb71d ("[SCSI] zfcp: Introduce experimental support for DIF/DIX")
Cc: <stable@vger.kernel.org> #2.6.36+
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_fsf.c

@@ -2257,7 +2257,8 @@ int zfcp_fsf_fcp_cmnd(struct scsi_cmnd *scsi_cmnd)
 	fcp_cmnd = (struct fcp_cmnd *) &req->qtcb->bottom.io.fcp_cmnd;
 	zfcp_fc_scsi_to_fcp(fcp_cmnd, scsi_cmnd, 0);
 
-	if (scsi_prot_sg_count(scsi_cmnd)) {
+	if ((scsi_get_prot_op(scsi_cmnd) != SCSI_PROT_NORMAL) &&
+	    scsi_prot_sg_count(scsi_cmnd)) {
 		zfcp_qdio_set_data_div(qdio, &req->qdio_req,
 				       scsi_prot_sg_count(scsi_cmnd));
 		retval = zfcp_qdio_sbals_from_sg(qdio, &req->qdio_req,